Class 6 Physics - BeTOPPERS IIT / NEET Foundation Series - 2022 Edition

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IIT FOUNDATION Class VI

PHYSICS

© USN Edutech Private Limited The moral rights of the author’s have been asserted. This Workbook is for personal and non-commercial use only and must not be sold, lent, hired or given to anyone else.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior written permission of USN Edutech Private Limited. Any breach will entail legal action and prosecution without further notice.

Utmost care and attention to the details is taken while editing and printing this book. However, USN Edutech Private Limited and the Publisher do not take any legal responsibility for any errors or misrepresentations that might have crept in.

Published by

:

USN Eductech Private Limited, Hyderabad, India.

PREFACE Our sincere endeavour in preparing this Book is to enable students effectively grasp & understand the Concepts of Physics and help them build a strong foundation in this Subject. From among hundreds of questions being made available in this Book, the Student would be able to extensively practice in each concept exclusively, throughout that Chapter. At the end of each Chapter, two or three Worksheets are provided with questions which shall cover the entire Chapter, helping each Student consolidate his / her learning. This Book help students prepare for their respective Examinations including but not limited to i.e. CBSE, ICSE, various State Boards and Competitive Examinations like IIT, NEET, NTSE, Science Olympiads etc. It is compiled by our inhouse team of experts who have a collective experience of more than 40 years in their respective subject matter / academic backgrounds. This books help students understand concepts and their retention through constant practice. It enables them solve question which are ‘fundamental / foundational’ as well questions which needs ‘higher order thinking’. Students gain the ability to concentrate, to be self-reliant, and hopefully become confident in the subject matter as they traverse through this Book. The important features of this books are: 1.

Lucidly presented Concepts: For ease of understanding, the ‘Concepts’ are briefly presented in simple, easy and comprehensible language.

2.

Learning Outcomes: Each chapter starts with ‘Learning Outcomes’ grid conveying what the student is going to learn / gain from this chapter.

3.

Bold-faced Key Terms: The key words, concepts, definitions, formulae, statements, etc., are presented in ‘bold face’, indicating their importance.

4.

Tables and Charts: Numerous strategically placed tables & charts, list out etc. summarizes the important information, making it readily accessible for effective study.

5.

Box Items: Are ‘highlighted special topics’ that helps students explore / investigate the subject matter thoroughly.

6.

Photographs, Illustrations: A wide array of visually appealing and informative photographs are used to help the students understand various phenomena and inculcate interest, enhance learning in the subject matter.

7.

Flow Diagrams: To help students understand the steps in problem-solving, flow diagrams have been included as needed for various important concepts. These diagrams allow the students visualize the workflow to solve such problems.

8.

Summary Charts: At the end of few important concepts or the chapter, a summary / blueprint is presented which includes a complete overview of that concept / chapter. It shall help students review the learning in a snapshot.

9.

Formative Worksheets: After every concept / few concepts, a ‘Formative Worksheet’ / ‘Classroom Worksheet’ with appropriate questions are provided from such concept/s. The solutions for these problems shall ideally be discussed by the Teacher in the classroom.

10. Conceptive Worksheets: These questions are in addition the above questions and are from that respective concept/s. They are advised to be solved beyond classroom as a ‘Homework’. This rigor, shall help students consolidate their learning as they are exposed to new type of questions related to those concept/s.

11. Summative Worksheets: At the end of each chapter, this worksheet is presented and shall contain questions based on all the concepts of that chapter. Unlike Formative Worksheet and Conceptive Worksheet questions, the questions in this worksheet encourage the students to apply their learnings acquired from that entire chapter and solve the problems analytically. 12. HOTS Worksheets: Most of the times, Summative Worksheet is followed by an HOTS (Higher Order Thinking Skills) worksheet containing advanced type of questions. The concepts can be from the same chapter or as many chapters from the Book. By solving these problems, the students are prepared to face challenging questions that appear in actual competitive entrance examinations. However, strengthening the foundation of students in academics is the main objective of this worksheet. 13. IIT JEE / NEET Worksheets: Finally, every chapters end with a IIT JEE / NEET worksheet. This worksheet contains the questions which have appeared in various competitive examinations like IIT, NEET, AIEEE, EAMCET, KCET, TCET, JIMPER, BHU, AIIMS, CBSE, ICSE, State Boards, CET etc. related to this chapter. This gives realtime experience to students and helps them face various competitive examinations. 14. Different Types of Questions: These type of questions do appear in various competitive examinations. They include:

• Objective Type with Single Answer Correct

• Non-Objective Type

• Objective Type with > one Answer Correct

• True or False Type

• Statement Type - I (Two Statements)

• Statement Type - II (Two Statements)

• MatchingType - I (Two Columns)

• MatchingType - II (Three Columns)

• Assertion and Reasoning Type

• Statement and Explanation Type

• Roadmap Type

• FigurativeType

• Comprehension Type

• And many more...

We would like to thank all members of different departments at BeTOPPERS who played a key role in bringing out this student-friendly Book. We sincerely hope that this Book will prove useful to the students who wish to build a strong Foundation in Physics and aim to achieve success in various boards / competitive examinations. Further, we believe that as there is always scope for improvement, we value constructive criticism of the subject matter, as well as suggestions for improving this Book. All suggestions hopefully, shall be duly incorporated in the next edition. Wish you all the best!!!

Team BeTOPPERS

CONTENTS 1.

Measurement

..........

01 - 10

2.

Motion and Force

..........

11 - 22

3.

Energy and Work

..........

23 - 44

4.

Light

..........

45 - 60

5.

Electricity

..........

61 - 76

6.

Magnetism

..........

77 - 90

7.

Heat

..........

91 - 95

8.

Key and Answers

..........

96 - 126

By the end of this chapter, you will understand

•

Measurement

•

Measurement of Area

•

Systems of units

•

Measurement of mass

•

Measurement of length

•

Measurement of Time

2. Systems of Units

1. Measurement

There are mainly ‘3’ system of units to measure length, mass and time.

Physics is inherently a science of measurement. The act of measuring a quantity required is called measurement.

I.

Chapter -1

Measurement

Learning Outcomes

Physical Quantity

System C.G.S F. P. S M.K.S

Any quantity that is measurable in physics is known as a Physical Quantity. Examples: Length, Mass, Time

II. Unit Measurement of a physical quantity means comparing it with known standard quantity. Each accepted standard quantity is the standard of measurement and commonly called unit.

III. Non Standard Units In early days, people used to measure length with the help of parts of body, such as outstreched palm, foot, arm or cubit.

Length Centimetre Foot Metre

Mass Gram Pound Kilogram

Time Second Second Second

M.K.S system is also known as Standard International (S.I) system. The details of which you will be studying in higher classes.

I.

Metric System C.G.S and M.K.S systems are known as Metric systems. British system F.P.S system is known as British system.

II. Simple multiples of Units Units used for the measurement of larger distances are the multiples of SI unit. For example: deca, hecto, kilo. 1 deca = 10 1 hecto = 100 1 kilo = 1000

Handspan

III. Sub-multiples of Units Footspan

Cubit

Such units cannot serve as standard for measuring length because they are going to be different for different people.

IV. Standard unit The measured value which is same when measured by anybody at any place is known as standard unit. Fundamental Measurements Measurement used to measure length, mass and time are called fundamental measurements or basic measurements.

Units used for measuring smaller distances are the sub-multiples of SI units. For example: milli, centi, deci.

1 deci =

1 10

1 centi =

1 100

1 milli =

1 1000

6th Class Physics

2

Formative Worksheet 1.

2.

3.

4.

5.

6.

7.

8.

What do we need to measure physical quantities accurately? (A) Standard units (B) Standard instruments (C) Both (A) and (B) (D) None of these Measurement has two parts they are ? (A) number and unit(B) unit and number (C) direction and unit (D) direction and number The standard used to measure a certain Physical quantity is (A) Unit (B) Scale (C) Both (1, (B) (D) None of these Pace or a footstep is a (A) MKS unit of length (B) CGS unit of length (C) FPS unit of length (D) Non standard unit of length Statement - I : Cubit is a standard unit Statement - II : 10 Kilometre = 1000 metre (A) Statement I is true ; Statement II is true. (B) Statement I is true ; Statement II is false. (C) Statement I is false ; Statement II is true. (D) Statement I is false ; Statement II is false. Statement I : Micro, milli, etc., are to be used as prefixes for metre only. Statement II : Kilogram is a standard unit. (A) Statement I is true ; Statement II is true. (B) Statement I is true ; Statement II is false. (C) Statement I is false ; Statement II is true. (D) Statement I is false ; Statement II is false. Basic (or) fundamental measurements are ? (A) Length, Mass and Time (B) Length, Area and Time (C) Length, density and Time (D) Density, volume and Time M.K.S system is also named as ? (A) Metric system (B) C.G.S system (C) British system (D) S.I system

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Conceptive Worksheet 1. 2.

3.

4.

5.

6.

7.

8.

Pick the odd man out: (A) Length (B) Metre(C) Yard (D) Cubit Number of fundamental physical quantities in M.K.S system are: (A) Two (B) Three(C) Seven (D)Six Cubit is a (A) MKS unit of length (B) CGS unit of length (C) FPS unit of length (D) Non standard unit of length Which of the following is a standard unit of length? (A) Decimetre (B) Centimetre (C) Millimetre (D) Metre. F.P.S stands for (A) Foot, pound, second (B) France, Paris, Spain (C) Force, pressure. second (D) Foot, Pace, Second C.G.S stands for : (A) Centimetre, gravitation, second (B) Centisecond, gram, second (C) Centimetre, gram, second (D) None of these Multiples and submultiples of units. (A) Are specific numerical values (B) Are used as prefixes (C) Both (A) and (B) (D) None of these Micro means (A) unit of time (B) 10,00,000 (C)

9.

1 10, 00, 000

(D)

1 milli

Pick the odd man out. (A) milli (B) kilo (C) micro (D) centimetre

3. Measurement of Length Length is the distance between two fixed points.

SI unit - metre(m) C.G.S unit - centimetre(cm) The various units used to measure length are m, mm, c, m, km etc. The inter-relationship among these units with a standard unit: 1 micro metre = 1 m = 10–6 m 1 millimetre = 1mm = 10-3m 1 centimetre 1cm = 10-2m 1kilometre = 103m

Mesurement

I.

3

Least Count The smallest quantity that can be measured accurately using any instrument is known as least count of that instrument. Least count of regular scale (LC) = 1mm =

1 cm 10

Mesurement of curved lines can be done by using a piece of thread. Thickness of coin by a centimetre scale or millimetre scale is Thickness of one coin =

Thickness  cm or mm  of 'n ' of coins Number of coins  n 

Diametre of a wire Diameter =

Length of the coins Number of turns in the coil

The diameter of spherical object can be measured by placing the object between two wooden blocks as shown in the figure.

10. The number of rounds of a wire around a pencil are 24 and the length of the coil is 4.8cm then what is the diameter of wire ? (A) 24 cm (B) 2.4 cm (C) 20 cm (D) 0.2 cm 11. The distance between Radha’s home and her school is 3250 m. Express this distance into km. (A) 32.5 km (B) 3.25 km (C) 0.325 km (D) 0.0325 km 12. The height of a person is 1.65 m. Express this value in mm. (A) 16.5 mm (B) 165 mm (C) 1650 mm (D) 16500 mm 13. While measuring the diameter of the ball, the inner edges of the wooden block stood at 3.4cm and 4.7cm on a scale. Calculate the diameter of the ball ? (A) 1.3 cm (B) 7.7 cm (C) 0.13 cm (D) 0.77 cm 14. Fill in the blanks (A) 1 cm = mm. (B) 1 dm = metre. (C) 1 kilometre = metre. (D)1metre = centimetre. 15. Fill in the blanks with < or > sign. (A) 1 decametre 1 decimetre. (B) 1 millimetre 1 centimetre. (C) 1 hectometre 1 kilometre. (D) 1 decimetre 1 centimetre.

Conceptive Worksheet 10.

11.

12. The diameter of spherical object = x2 – x1

II. Measurement of very large Distances Distance between earth and moon, or earth and sun can’t be done by using conventional units. Such large distances are expressed using following units.

III. Astronomical Unit(A.U) It is the average distance of the earth from the sun. 1 A.U = 1.496 × 1011m

Formative Worksheet 9.

In decreasing magnitude which of the following is correct ? (A) km, cm, m, mm (B) km, m, cm, mm (C) m, km, cm, mm (D) km, cm, mm, m

13.

14. 15.

What is the SI unit of length? (A) Metre (B) Centimetre (C) Kilometre (D) All of these 4 kilometre are equal to (A) 4, 00, 000 metre (B) 40, 000 metre (C) 4, 000 metre (D) 400 metre 15 cm are equal to (A) 150 mm (B) 15mm (C) 1.5 mm(D) 0.15 mm Which is a correct relationship? (A) 1m= 100 cm (B) 1 cm = 10 mm (C) 1 km = 1000 m (D) all the correct 1 cm = _________ kilometre. (A) 100 (B) 105 (C) 10–5 (D) 10–2 Arrange the following lengths in their increasing magnitude: 1 metre, 1 centimetre, 1 kilometre, 1 millimetre. (A) 1 centimetre < 1 millimetre < 1 kilometre < 1 metre (B) 1 millimetre < 1 centimetre < 1 metre < 1 kilometre (C) 1 kilometre < 1 metre < 1 centimetre < 1 millimetre (D) none www.betoppers.com

6th Class Physics

4 16. 1 Angstrom = ____ ? (A) 10-10m (B) 10-8m (C) 10-6mm (D) 10-10cm 17. 1AU = ? (A) 1.496 × 1011m (B) 1.496 × 109cm (C) 1.496 × 108m (D) 1.444 × 106m 18. The size of bacteria is generally measured in microns. The micrometre  μ m  , is often called the micron. How many microns make up 1 kilometre ? (A) 103 (B) 106 9 (C) 10 (D) 1012 19. Least count of a metre scale is ? (A) 1cm (B) 0.1mm (C) 0.1cm (D) 0.01mm

4. Measurement of Area Area is the amount of surface occupied by an object or a place. Area of a regular surface like a rectangle or a square can be calculated by using formula knowing its length and breadth (or) length of its side. Area = length × breadth The SI unit of area is m2 or square metre. The other units of area are cm2, mm2, km2 etc. Larger areas are measured in ‘acre’ and ‘hectare’. (1acre = 100m2, 1hectare = 100acre). For measuring bigger areas, such as area of fields or towns hectare is used. Area of an irregular surface is measured by using a graph paper as there is no formula for finding area of irregular shapes.

Formative Worksheet 16. What is the area of rectangular graph paper having 6cm length and 5cm width ? (A) 11 cm2 (B) 1 cm2 (C) 30 cm2 (D) 60 cm2 17. The length of a school compound is 450m and breadth is 145m. Find the area of compound hectare? (A) 6525 hectare (B) 652.5 hectare (C) 65.25 hectare (D) 6.525 hectare 18. 1 m2 = ______x_______hectare. 1 hectare = _____y_____ km2 . 1 mm2 = _____z_____ km2. (A) x = 10–6, y = 10–4, 10–2 (B) x = 10–4, y = 10–2, z = 10–6 (C) x = 10–2, y = 10–4, z = 10–6 (D) 10–4, y = 10–6, z = 10–2 www.betoppers.com

19. A school hall measures 20 m in length and 12 m in breadth. Find the area of the school hall. (A) 1200 m2 (B) 120 m2 (C) 240 m2 (D) 2400 m2

Conceptive Worksheet 20. Area of 1sqcm is ? (A) 100mm2 (B) 1000mm2 2 (C) 10mm (D) 10,000mm2 21. How many small squares are there in 1sq.cm ? (A) 1000 (B) 100 (C) 10 (D) 1 22. Area of irregular shaped bodies are measured using ? (A) Graph paper (B) Scale (C) Using formula (D) Tape 23. The area of the land is 100m2, here m2 stands for (A) Numerical value of area (B) Unit of area (C) Both (A) and (B) (D) None of these 24. 1km2 = _____________ (A) 1 hectare (B) 10 hectares (C) 100 hectares (D) 1000 hectares 25. 1 hectare = ____________ (A) 1000m2 (B) 10000m2 (C) 100000m2 (D) 100m2

5. Measurement of Volume The space occupied by a substance (solid, liquid or gas) is called volume. volume = length × breadth × height S.I unit of volume - m3(cubic metre) C.G.S unit of volume - cm3(centimetre cube) Volume of regular shape like a cuboid = length × breadth × height Volume of irregular bodies cannot be measured by formula. They can be calculated by using measuring jar and overflow jar . Measurement of volume of liquid To measure the volume of liquids measuring jars can be used directly.

Different Measuring Jars Measuring jar: It is used to measure the liquids of desired quantity. Measuring Vessels: They are used to measure volume of liquids like milk and oil. Pipette: It is used in laboratories to take specific volume of liquid. Burette: It is also used in laboratories to extract required volume of liquid for the experiment.

Mesurement

Formative Worksheet 20. Find the volume of cuboid of dimensions 5cm, 4cm and 3cm ? (A) 60 cm3 (B) 120 cm3 3 (C) 240 cm (D) 480 cm3 21. A measuring cylinder has 75cm3 of water, when a stone is droped water level rises to 125cm3. What is the volume of stone ? (A) 25 cm3 (B) 50 cm3 3 (C) 75 cm (D) 100 cm3 22. A stone of volume 50cm3 lowered into 80cm3 of water in a measuring jar. Then what will be the new reading in measuring jar ? (A) 15 cm3 (B) 30 cm3 (C) 45 cm3 (D) 60 cm3 23. The volume of a rectangular slab is 12 cm3. The length and breadth of the slab are 3 cm and 2 cm respectively. Find its height. (A) 10 cm (B) 8 cm (C) 4 cm (D) 2 cm 24. A boy has purchased a toy, which is in the form of a cuboid. The cuboid has the following dimensions: 0.003 km × 0.03 m × 3 cm. What is volume of this cuboid? (A) 900 cm3 (B) 1800 cm3 3 (C) 2700 cm (D) 3600 cm3 25. When a stone is lowered into a measuring cylinder containing water, the volume becomes 9.3 ml. If the volume of the stone is 5.8 ml, find the initial volume of water in the measuring cylinder. (A) 3.5 ml (B) 5 ml (C) 6.5 ml (D) 8.5 ml 26. Express 5cm3 in terms of cubic millimetres (A) 500 mm3 (B) 5000 mm3 3 (C) 50 mm (D) 0.5 mm3

Conceptive Worksheet 26. The space inside a regular or irregular objects is known as ? (A) Area (B) Volume (C) Mass (D) Length 27. The unit for the volume of solids in SI ? (A) cm3 (B) m3 (C) ml3 (D) l3 28. 1cubic meter is ? (A) 106cc (B) 104cc (C) 103cc (D) 109cc 29. In laboratories to take specific volume of liquid we use ? (A) Pipette (B) Burette (C) Measuring jar (D) Measuring vessel

5 30. 1 litre = ? (A) 1000cc

(B) 1000cm

(C) 100ml

(D) 100cm

31. The space occupied by a substance is called _________. (A) Area

(B) Length

(C) Volume

(D) None of these

32. The S.I unit of volume is _________ (A) Cubic centimetre(B) Cubic millimetre (C) Cubic metre

(D) Cubic litre

33. One cubic metre is equal to ––––– (A) 106 cc

(B) 104 cc

(C) 103 cc

(D) 109 cc

34. The volume occupied by a cube whose each side is equal to 1cm is called (A) Cubic centimetre (B) Cubic millimetre (C) Cubic metre (D) None of these

6. Measurement of Mass Mass is the amount of matter contained in a body. Mass is measured using devices like common balance, physical balance etc., SI unit of mass is kg. The other units of mass are milligram(mg), gram(g), tonne, quintal. 1mg = 10-3g 1quintal = 100kg 1tonne = 1000kg

7. Measurement of Time Time is the interval between two events. The SI unit of time is second. The different units of time are given below. 1mean solar day = 24hours 1min = 60seconds 1hour = 60seconds 1year = 365days 1decade = 10years 1century = 100years 1millenium

= 1000years www.betoppers.com

6th Class Physics

6

Summative Worksheet

Formative Worksheet 27. One quintal = ______________ton. (A) 10 (B) 100 (C) 0.1 (D) 0.01 28. 1 metric tonne = __________ milligram. (A) 103 (B) 106 (C) 109 (D) 1012 29. 1 microsecond = 10x milliseconds. Find x. (A) +1 (B) + 3 (C) –1 (D) –3 30. 1 kg = –––––––––– tonne. (A) 100 (B) 1000 (C) 10–3 (D) 10–2 31. A truck of weigh 4.4tonnes. Its value in kg? (A) 4400 kg (B) 440 kg (C) 44 kg (D) 4.4 kg 32. How many seconds are equal to 6hours 8min? (A) 86400 sec (B) 43200 sec (C) 1296480 sec (D) 648240 sec

1.

2.

3.

Conceptive Worksheet 35. 1mean solar day = ? (A) 365days (B) 10years (C) 24hours (D) 60minutes 36. Which of the following measurement have not correct expression in S.I unit ? (A) 5l cm cloth (B) 20sec of time (C) Surface area 40cm2 (D) 2kg water 37. 1quintal = ? (A) 100kg (B) 1000kg (C) 10kg (D) 500kg 38. If the Charminar superfast express staying 00 hours in Warangal, then the time in 12 hour clock is _________ (A) 12 0’ clock at night (B) 12 0’ clock at noon (C) 18 0’ clock at night (D) 18 0’ clock at noon 39. A passenger goes to Secunderabad railway station. He asked the enquiry counter, “When did Tirumala express come?” The enquiry counter person replied “18 hour 15 minutes.” Then the time in his 12-hour clock was ________. (A) 5 hour – 45 minutes AM (B) 5 hour – 45 minutes PM (C) 6 hour – 15 minutes AM (D) 6 hour – 15 minutes PM

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4.

5.

6.

7.

8. 9.

Statement I: A thread is enough to measure a curved line. Statement II: A scale is enough to measure a curved line. (A) Statement I is true ; Statement II is true. (B) Statement I is true ; Statement II is false. (C) Statement I is false ; Statement II is true. (D) Statement I is false ; Statement II is false. To measure the length of a curved line, which of the following materials are needed ? (A) Cotton thread (B) Measuring scale (C) Common balance (D) Watch In which of the following, are indirect methods of measurement used? (A) Measuring thickness of a wire (B) Measuring thickness of a coin or plate (C) Measuring length of table (D) All Metre scales have _________________ ends to avoid error due to ________________ (A) Cylindrical, Volume of the scale (B) Tapered, thickness of the scale (C) Tapered, Area of the scale (D) Cylindrical, Area of the scale 1cm2 = _____________ (A) 10–10 km2 (B) 10–8 hectare –4 2 (C) 10 m (D) all of these 2 1m = ___________ (A) 10–6 km2 (B) 10–4 hectare –2 (C) 10 are (D) all of these When do we say that a bucket is bigger than a cup? (A) When the volume of cup is greater than the volume of bucket. (B) When the volume of bucket is greater than the volume of cup. (C) When the volume of bucket is equal to the volume of cup. (D) We can’t say. Pick the odd man out. (A) mega (B) kilo (C) tonne (D) hecta The length of a school compound is 450m and breadth is 145m. The area of the school compound in hectares is ________ (A) 6.525 hectares (B) 65.25 hectares (C) 0.6525 hectares (D) 652.5 hectares

Mesurement

7

10. If an aeroplane is scheduled to take off at 18 hours – 57 minutes, then time in PM on a 12 - hour clock is __________ (A) 12 - hour – 57 minute AM (B) 12 - hour – 57 minute PM (C) 6 - hour – 57 minute AM (D) 6 - hour – 57 minute PM

HOTS Worksheet 1.

2. 3.

Under the spout of over flow jar, place a measuring cylinder. Gently lower a stone in the over flow jar. The stone displaces water which flows out from the spout into the measuring cylinder. If the reading on the overflow jar is 12ml, then the volume of stone is __________. (A) 12 × 10–5 m3 (B) 1.2 × 10–5 m3 (C) 0.12 × 10–5m3 (D) 0.012 × 10–5m3. One millennium is equal to how many decades? (A) 10 (B) 100 (C) 1000 (D) 10, 000 D

C

1 cm

1 cm

7.

1 year = _____________ seconds (A) 315. 36 × 106 (B) 3.1536 × 106 (C) 31. 536 × 106 (D) 3153. 6 × 106 8. A syringe has a capacity of 5 ml. Its capacity in cm3 and m3 is respectively are (A) 5 × 10–6 m3, 5 cm3 (B) 5 cm3, 5 × 10–6 m3 (C) 5 × 10–3 m3, 5 cm3 (D) 5 cm3, 5 × 10–3 m3 9. A water tank has a capacity of 10, 000 litre. Its value in m3 is (A) 100 m3 (B) 1000 m3 (C) 1 m3 (D) 10 m3 10. The water level of a measuring cylinder is 26 ml. A piece of concrete having a volume of 6 cm3 is immersed in it. The new level of water is (A) 20 ml (B) 26 ml (C) 32 ml (D) 6 ml 11. The mass of an electron is 9.11 × 10–31kg. How many electrons would make 1kg? (A) 1.1 × 1030 (B) 1.1 × 1031 (C) 1.1 × 10–30 (D) 1.1 × 10–31 12. If m1, m2, m3 and m4 are masses of four bodies 0.3 kg, 0.3 mg, 0.3 × 10–6 g and 3000 g respectively. The above, in increasing order of masses, are as follows. (A) m1 > m2 > m3 > m4 (B) m4 > m2 > m3 > m4 (C) m4 > m1 > m2 > m3

(D) m3 > m2 > m4 > m1

IIT JEE Worksheet B

A

4.

5.

6.

Let ABCD be a centimetre graph paper. The area of darkened surface on the graph paper is _______________ (A) 8 cm2 (B) 11 cm2 (C) 9cm2 (D) 10cm2 If the time on a 12 - hour clock is 3 hour – 45 min PM, then time on 24 - hour clock is _____ (A) 15 hour – 45 minutes (B) 15 hour – 12 minutes (C) 6 hour – 57 minutes (D) 12 hours 1 day = _____________ millennium (A)

1 165000

(B)

1 265000

(C)

1 46400

(D)

1 365000

1 decade = _____________ minutes (A) 52. 56 × 106 (B) 5. 256 × 106 (C) 525. 6 × 106 (D) 5256 × 106

I.

Single Correct Answer Type

1.

Chand goes to a hospital for a health checkup. There, he is asked to stand in front of a meter scale, so that his height could be measured. 2

1

210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10

(A) 1 m and 100 cm(B) 1 m and 11 cm (C)1 m and 10 cm (D) 1 m and 1 cm www.betoppers.com

6th Class Physics

8 II. 3.1 mm = 0 0

1

2

3

4

1

5 2

6

7

8

9

3

10

The information in which alternative completes the given statement?

4

I

2. 0 0

1

2

3

4

1

5 2

6

7

8

9

3

10

II

3.

I 0

4.

5.

6.

7.

1

II 2

3

4

5

6

7

8

9

10

The relative change in the position of the ants is (A) 1 cm (B) 2 cm (C) 5 cm (D) 9 cm Which of the following tools must be used to find the tallest student in a group of four? (A) Clock (B) Thermometer (C) Measuring tape (D) Weighing balance Sandeep has a wooden study table. He wants to measure the height of the table. Which of the following tools can be used by Sandeep to measure the height of his study table? (A) Measuring tape (B) Pan balance (C) Microscope (D) Telescope Peter has to run a distance of 200 m. He can run a distance of 10 m in one second. If Peter runs at this rate, then he can cover 200 m in (A) 22 s (B) 20 s (C) 18 s (D) 13 s Fill in the blanks. I. 2.4 cm =

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 mm

(A)

i ii 240 3.1 × 10- 3

(B)

i ii 240 3.1 × 10- 6

(C)

i 24

ii 3.1 × 10- 3

(D)

i 24

ii 3.1 × 10- 6

4

The respective lengths of pencils I and II are (A) 4.5 mm and 3 cm (B) 4.5 cm and 3 cm (C) 4.5 mm and 3 mm (D) 4.5 cm and 3 mm Two ants are moving on a ruler, as shown in the given figure. Initially, the ants are at position I. After some time, the ants are at position II.

 km

8.

The length of a thread is 10-hand spans. It is used to measure the circumference of a solid cylinder. For this purpose, the thread is wound around the circumference of the cylinder. If the thread is wound around the cylinder five times, then what is the circumference of the cylinder? (A) One-hand span (B) Two-hand spans (C) Five-hand spans (D) Ten-hand spans 9. The height of an ice pole is 120 cm. In every half hour, the height of the pole reduces to half its length as the ice melts. What will be the height of the pole after two hours? (A) 15 mm (B) 30 mm (C) 60 mm (D) 75 mm 10. Akram has a piece of thread. He measures the length of a table using this thread. He has to place the thread eight times along the length of the table to measure its length. Then, he folds the thread twice at its midpoint and again measures the length of the same table. How many times does Akram have to place the folded thread along the length of the table? (A) 4 (B) 8 (C) 16 (D) 32

II. Multiple Correct Answer Type 11. Which of the following is the unit of length? (A) Metre (B) Centimetre (C) Foot (D) second 12. Which of the following is the unit of area? (A) cm2 (B) mm2 (C) m2 (D) m/s2 13. Which of the following is the unit of mass? (A) pound (B) metere (C) gram (D) ton 14. Which of the following is the unit of volume? (A) cubic metre (B) mm2 3 (C) cm (D) (foot)3

Mesurement

9 23. The length of a blackboard is 240 cm. Rakesh tries to measure this length using a small wooden stick of length 40 cm. The number of times that the stick must be revolved over the blackboard to completely cover the length is __________.

III. Paragraph Type 1 deci =

1 10

1 centi =

1 100

1 milli =

1 1000

15. 1 decimetre = (A) 10–3 m (C) 10–1 m 16. 1 milligram (A) 10–3 g (C) 10–1 g 17. 1 cm3 (A) 10 mm 3 (C) 103 mm 3 18. 1 km2 (A) 103 m 2 (C) 1012 m 2 19. 1 milli second (A) 10–3 s (C) 10–3 s

V. Matrix Matching Column I

24.

(B) 10–2 m (D) 10 m

Column II

(A)

1 Hectogram

p)

10- 6 gram

(B)

1 Decagram

q)

102 gram

(C)

1milli gram

r)

10 gram

(D)

1 micro gram

s)

10- 3 gram

–2

(B) 10 g (D) 10 g (B) 102 mm 3 (D) 106 mm 3

25. Column I Column II (i) Volume of a swimming pool (a) cm3 (ii) Volume of a glass filled with milk(b) m3 (iii) Volume of an exercise book (c) litre (iv) Volume of air in a room (d) millilitre

(B) 106 m 2 (D) 1015 m 2 (B) 10–2 s (D) 10–6 s

IV. Integer Type 20. Radha sees her mother cleaning the room with broom. She takes two broomsticks of different lengths and decides to measure the length of her room. She finds that the length of the room is 18 times the length of the shorter stick. The length of the shorter stick is half the length of the other stick. How many longer sticks will be required to fit along the length of the room? 21. Swati has three dolls. She names them as Reena, Teena, and Meena. She then takes a metre scale and measures their heights. She observes that: I. Reena is taller than Teena by 5 cm. II. Meena is shorter than Reena by 4 cm. If the height of Meena is 0.55 m, then Meena is taller than Teena by ______cm. 22. Ramesh measures the length of a thread and finds it to be 14hand-spans. He uses it to measure the circumference of a rectangular table. He wounds the thread around the circumference of the table. If the thread is wound around the table two times, then the circumference of the table is ________ hand spans.

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10

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6th Class Physics

By the end of this chapter, you will understand

1.

•

Types of Motion

•

Effects of Force

•

Rest & Motion

•

Contact Forces

•

Types of Motion

•

Non Contact Force

•

Forces

•

Other Force

2.

Rest & Motion

I.

Rest A body is said to be at rest if it does not change its position with respect to the reference point. The objects which remain stationary at a place and do not change their position are said to be at rest. Example : A table and chairs lying in a room are in the state of rest, because they do not change their position with respect to the surroundings of the room.

II.

Example: A vehicle has to be driven. Rain drops fall due to gravitational pull.

Introduction Mechanics is the branch of physics that focuses on the motion of objects and the forces that cause the motion to change. There are two branches of Mechanics: Kinematics and Dynamics. The word kinematics comes from the Greek word “Kinema” meaning motion. The word dynamics comes from the Greek word “dynamis” meaning power. Kinematics deals with the concepts that are needed to describe motion without any reference to forces or the cause of the motion. The goal of study of kinematics is to develop sophisticated mental models, which serve us in describing the motion of real world objects. Dynamics deals with the relation between the forces and the motion. The motion of objects can be described by words such as distance, displacement, speed, velocity and acceleration. Before we witness the concepts of kinematics, let’s review some basic concepts.

Motion An object is said to be in motion if it changes its position from one place to another. In other words, the movement of an object is known as the motion of the object.

Chapter -2

Motion & Force

Learning Outcomes

3.

Types of Motion All bodies in motion do not move the same way. For example, a car moves straight along the road; a spinning top spins round and round; the strings of a sitar move up and down and the pendulum of a clock moves sideways in either direction. The motion of bodies is classified as under:

I.

Translatory Motion The motion in which all the particles of a body move through the same distance in the same time is called translatory motion. Examples : i) A car or a train moving along a road or track. ii) A ball rolling on the ground. iii) Firing of a bullet from a gun. iv) A stone hurled from a catapult. vii) An apple falling from a tree. viii) A striker on the carom board going straight to hit the coin, etc. There are two kinds of translatory motion: (a) Rectilinear motion and (b) Curvilinear motion.

a)

Rectilinear Motion When an object moves along a straight line like a ball dropped from a height, the motion described by the body is called rectilinear motion. Examples: i) A ball rolling on the ground. ii) A car moving on a straight road. iii) A stone falling freely from the roof of a building. iv) A coin moving over a carom

board.

6th Class Physics

12

b)

Curvilinear Motion

When a body moves along a curved path, the motion described by the body is called curvilinear motion. Examples: i) A stone thrown by a boy from a height. ii) A car moving along a curved path. iii) A javelin or shot-put thrown by an athlete. iv) A ball thrown upward at an angle. v) A car or train moving along a curved road or track are all examples of curvilinear motion.

II.

III.

When a body moves around a circular path, the way an athlete runs around a circular track, such motion is called circular motion. Examples: i) Motion of an electric fan. ii) Motion of a merry-go- round. iii) Motion of a spinning top. iv) Motion of the earth around the sun. Note:In circular motion, the position of a body itself keeps changing with time, but in rotational motion the position of a body does not change. It is to be noted that circular motion is a special case of rotatory motion.

Rotational Motion A motion in which a body moves about a fixed axis without changing its position is called rotational motion. Examples: i) The motion of the blades of a fan. ii) The wheel of a sewing machine. iii) The motion of a giant wheel. iv) A spinning top v) A spinning wheel (charkha) vi) A rotating potter’s wheel

Combination of Translatory and Rotational Motion In some cases, the motion of rotation and the motion of translation occur at the same time. When a drill cuts through a metal piece, it performs the motion of translation as well as the motion of rotation at the same time. Other examples of this kind of motion are the wheels of a moving bicycle or a car, the ball delivered by a spin bowler.

IV.

Rotational Motion

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Comparision of Rotational and Circular Motions Rotational Motion Circular Motion 1. Body stays in 1. Body doesn’t same place with stay in same moves and place. It changes its respect to position w ith time. time. 2. The body 2. It moves rotates about an along a path axis may not whose axis pass through passing the body. through it. 3. No linear 3. Body may mot ion is undergo linear observed for motion. the body as a whole.

Oscillatory Motion

A motion in which the body as a whole moves toand-fro about its mean position is called oscillatory motion. Examples : i) The movement of a swing. ii) The oscillation of pendulum of a clock. iii) The needle of a sewing machine moving up and down. iv) The piston of a motor car, the pressing cylinder of a juice machine, the piston of a spray pump etc.

Translational Motion

A moving bicycle describes both translational and rotational motion

Circular Motion

V.

Vibratory Motion It is another kind of oscillatory motion in which the body does not move as a whole i.e. the entire object does not move but undergoes change in shape or size.

Motion & Force

13 Examples: i) When a spin bowler delivers a ball, the ball has a motion of spin (rotatory motion)while it moves towards the batsman (translatory motion).

Examples: i) When you pluck a string of a guitar or sitar, it vibrates to and fro about its position of rest and produces music. ii) When you strike the membrane of a drum, it vibrates up and down about its position of rest and produces sound. T hese vibrations are like the oscillations of a pendulum, except that they are faster. There is another difference. The pendulum swings freely, while the string of a musical instrument is fixed at two ends, and the membrane of a drum is fixed around the circumference of the drum. iii) During breathing, when our chest expands or contracts, the motion is vibratory in nature; all the points on the chest do not move out equally.

VI.

Linear Motion of the ball

A spinning ball

ii)

iii)

Periodic Motion A motion which repeats itself at regular intervals of time is called periodic motion. Examples: i) The motion of the earth round the sun is periodic. ii) The swinging pendulum of a wall clock. iii) The needle of a sewing machine running at constant speed. iv) The heart beat of a normal human being. v) The motion of a swing. vi) The movement of the lungs during breathing.

iv)

v)

vi)

VII. Random Motion A body which has a particular motion that suddenly changes to another kind of motion is said to have random motion. In other words, the motion without any sequence or direction is random motion. Examples : 1) A buzzing bee. 2) A football player on the field. 3) The motion of a hockey ball during a game. 4) The flying motion of a sparrow. 5) A monkey performing antics on a tree.

VIII. Multiple Motion Sometimes an object manifests two or more types of motion at the same time. Such motion is called multiple motion.

A person is drawing water from a well. Here, the pulley on which the rope runs has a rotatory motion while the bucket coming up has a translatory motion. A girl riding a bicycle. The wheels of the bicycle rotate (rotatory motion ) and at the same time the bicycle moves forward in a straight or curved path (translatory motion). A drill used by a carpenter for drilling a hole in wood, has both translatory and rotatory motions. This is because while it is being rotated (rotatory motion), it is also getting pushed forward (translatory motion) into the wood. The earth rotates about its axis (rotatory motion) and at the same time it revolves around the sun in a circular path (translatory motion). The mythological Sudarshan Chakra hurled by Lord Krishna to kill his enemies had both translatory as well as rotatory motion.

Formative Worksheet 1.

2.

3.

Which of the following is not making translatory motion ? (A) A ball delivered by a spin bowler (B) A brill that bores a piece of wood (C) Movement of toy car around circular path (D) Moving rear wheel of a bicycle on its stand The motion described by a football ? (A) Curvilinear (B) Circular (C) Oscillatory (D) Non-uniform Which of the following is a periodic motion ? (A) Freely falling body (B) A swinging pendulum (C) Bullet fired from the gun (D) A flying kite

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6th Class Physics

14 4.

Which of the following statement is not correct? (A) Needle of sewing machine undergoes circular motion (B) Motion of body thrown upward at an angle is curvilinear (C) Movement of the earth around the sun is circular (D) Ball dropped from a height is rectilinear 5. How are day and nights caused ? (A) Rotation of the earth (B) Gravitational force of earth (C) Mass of the earth (D) None 6. Which of the following is not an example of translatory motion ? (A) A freely falling stone (B) A coin moving over carom board (C) A car or train moving along a curved road or track (D) A ceiling fan 7. From the following pick out the example for rotatory motion ? (A) A spinning wheel (B) Merry-go-round (C) Blades of mixer grinder (D) All the above 8. Examples for the circular motion ? (A) Revolution of earth around the sun (B) Motion of the tip of the seconds hand of a wall clock (C) Both (D) None 9. Which of the following posses both rotatory and translatory motion ? (A) Motion of the wheels of a horse driven cart (B) When a drill bores a hole in a wooden piece (C) Ball delivered by a spin bowler (D) All the above 10. Motion of a bob of a simple pendulum ? (A) Rectilinear (B) Curvilinear (C) Periodic (D) Rotatory

4.

5. 6. 7. 8. 9. 10.

.

4.

2. 3.

Which of type of motion do the strings of the violin represent? Which type of motion is described by rolling ball ? All oscillatory motions are periodic by nature. Explain .

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Forces Many activities in our day to day life are associated with pushing or pulling. Therefore, whenever an object is moved, we can say that it has either been pushed or pulled. This push or pull is known as force. In other words, a body moves whenever a force is applied to it. Units of force: Force is measured in terms of Newton.

5.

Effects of Force Force cannot be seen, heard or tasted. Only its effects can be felt or seen. The various effects of force are: 1. It can move a body initially at rest. 2. It can bring a moving body to rest. 3. It can change the direction of a moving body. 4. It can change the speed of a moving body. 5. It can change the shape of a body. 6. It can change the size of a body.

6.

Contact Forces Forces acting between two bodies can be classified into two broad categories: Contact force and non-contact force. Contact forces are those that act between two objects, which are in direct contact with each other. The two common examples of contact forces are muscular and frictional.

Conceptive Worksheet 1.

Passengers sitting in a moving train are in _____ with respect to platform, but in _____ with respect to co-passengers in the train ? A body undergoing circular motion may also have linear motion. Explain. A book lying on the table is at___ . A body is said to be in _____ if it changes its position with respect to surroundings with time. Can a body execute both rotatory and translatory motion simultaneously ? Motion of pendulum of a clock is an example of _____ motion. The heartbeat of a normal resting person is ____

I.

Frictional Force The force of friction acts between all moving bodies, which are in contact with one another. The force of friction always acts opposite to the direction of motion. The magnitude of this force depends on the nature of the surface in contact.

Motion & Force

NOTEWORTHY POINTS

15

II.

II.

Muscular Force The force applied by the action of muscles in our body is termed as muscular force. For example, when you pick up a book placed on the table using your hands, you apply muscular force. For lifting the book from the table using your hands, you had to touch the book. You cannot lift the book without making contact with it. Hence, muscular force is a contact force. Like humans, animals also use muscular force to perform various activities. For example, birds fly in the air by flapping their wings.

7.

Non Contact Force Non-contact forces are those forces that act between two objects, but are not in direct contact with each another. Examples of non-contact forces include magnetic force, electrostatic force and gravitational force.

I.

Electrostatic Force Take a paper and tear it into pieces. Now, rub a plastic scale against dry hair and bring this scale close to the paper pieces. What do you observe? You will observe that the pieces of paper are attracted towards the scale. This happens because rubbing of the scale against dry hair produces an electrostatic charge. Thus, the scale attracts the pieces of paper by a non-contact force known as electrostatic force.

1. Frictional force is a contact force. 2. Frictional force always acts between two moving objects, which are in contact with one another. 3. Frictional force always acts opposite to the direction of motion. 4. Frictional force depends on the nature of the surface in contact.

NOTEWORTHY POINTS 1. 2. 3.

4. 5.

III.

Electrostatic force is a non-contact force. Electrostatic force can be attractive as well as repulsive. Electrostatic force is the force that exists either between two charged bodies, or between a charged and uncharged body. Electrostatic force depends on the magnitude of charge present in the bodies. Electrostatic force also depends on the distance between the interacting bodies.

Gravitational Force Do you know why apples fall towards the ground from trees? Why does water from a tap flow down? The Earth attracts everything (that is near or on its surface) towards its centre by a non-contact force known as gravitational force. It is this force that makes an apple fall towards the ground from the tree and makes the water from a tap flow down.

Magnetic Force What will happen if you bring the South Pole of a bar magnet close to the North Pole of another bar magnet? The magnets will attract each other. They attract each other with magnetic force. What will happen if you bring the North Pole of both bar magnets close to each other? The bar magnets will repel each other. The force with which they repel each other is known as magnetic force.

NOTEWORTHY POINTS 1. 2. 3.

NOTEWORTHY POINTS 1. Magnetic force can be attractive as well as repulsive. 2. Magnetic force is a non-contact force. 3. Magnetic force acts between two magnets or between a magnet and a magnetic material (such as iron). 4. Magnetic force depends on the strength of the magnet used. 5. Magnetic force also depends on the distance between the interacting bodies.

4. 5.

Gravitational force is a non-contact force. Gravitational force is an attractive force. Gravitational force is the force that is exerted by the earth on every object, which is near or on its surface. Gravitational force depends on the mass of the body. Gravitational force also depends on the distance between the Earth and body.

8.

Other Force

I.

Consequential Forces A force which comes to play when a force is applied on an object. These forces donot exist on their own. Eg: When we stretch a spring or a rubber band, the consequential force of tension comes to play which tends to bring the spring or rubber band to its original shape. www.betoppers.com

6th Class Physics

16

II.

Centrifugal Force

17.

When a body is moving along a circular path, a force that acts always out wards to the circular path is called centrifugal force.

III.

Centripetal force When a body is moving along a circular path, the force that acts towards the centre of the circle is called centripetal force.

IV.

Elastic Spring Force

18.

A pulling or pushing force exerted on a spring can cause the spring to stretch or compress. This force is known as elastic spring force. It is elastic, because it allows the object to return to its original shape after being compressed or stretched.

19.

Formative Worksheet 11.

12.

13.

14.

15.

16.

Magnetic force is a ________. (A) Contact force (B) Force at distance (C) Consequential force (D) None of these Magnetic force causes ________. (A) Attraction (B) Repulsion (C) Both attraction and repulsion (D) None of these The S .I unit of force is ________. (A) Newton (B) Kilogram force (C) Gram force (gf) (D) Dyne The Force of friction is ________. (A) Always an advantage (B) Always a disadvantage (C) Sometimes an advantage and sometimes a disadvantage (D) Neither an advantage nor disadvantage Deep grooves in the tyres of a tractor : (A) Increase friction (B) Decrease friction (C) Make it stable (D) Make tyre more attractive Which of the following is not an effect of frictional force ? (A) Grooves of tyres flattering after months of travel on the road (B) A rolling ball coming to rest (C) Leaves falling to the ground (D) Holding a pencil in hand

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Which of the following is not an effect of force? (A) Forces can change the size of an object (B) Forces can change the direction of moving object (C) Forces can change the chemical properties (D) Forces can change the speed of a moving object Force of friction can be reduced by ? (A) Using lubricants (B) By polishing surfaces (C) By using ball-bearings (D) All the above Which force always attracts objects towards the earth ? (A) Gravitational force (B) Magnetic force (C) Frictional force (D) Contact force

Conceptive Worksheet 11.

12.

13.

14.

15.

16.

17.

18.

Force (A) An move a body initially at rest. (B) Can bring a moving body to rest. (C) Can change the shape of a body. (D) All Which of the following is a contact force? (A) Frictional force (B) Muscular force (C) Both (D) None Which of the following is a non contact force? (A) Frictional force (B) Muscular force (C) Magnetic force (D) All Which of the following is a not a contact force? (A) Magnetic force (B) Gravitational force (C) Electrostatic force (D) All The birds fly high in the sky due to (A) Magnetic force (B) Gravitational force (C) Muscular force (D) Frictional force Force is measured in (A) Metres (B) Seconds (C) Kilogram (D) Newton Electrostatic force is (A) Only attractive (B) Only repulsive (C) Both (D) None Apple falls down to earth from the tree when shook. This is due to (A) Magnetic force (B) Gravitational force (C) Muscular force (D) Frictional force

Motion & Force 19.

20.

17

A body in circular motion is acted upon by (A) Centripetal force (B) Centrifugal force (C) Both (D) None A spring stretches due to (A) Centripetal force (B) Gravitational force (C) Magnetic force (D) Elastic force

3.

The given figure shows a stone tied to a vertical rod using a rope. The stone is moving around the rod.

Summative Worksheet 1.

Two ants are moving on a ruler, as shown in the given figure. Initially, the ants are at position I. After some time, the ants are at position II.

The stone is moving in a (A) rectilinear motion (C) linear motion 4.

2.

(B) circular motion (D) wave motion

The motion of the tires of a bicycle is the bicycle’s motion is .

, while

The given statement is correctly completed by row

The relative change in the position of the ants is (A) 1 cm (B) 2 cm (C) 5 cm (D) 9 cm The given figure shows a cork placed on the surface of water in a tub. A small stone is dropped in the water. The cork star ts moving in a  motion caused by the motion produced on the surface of water.

5.

(A)

I linear

II circular

(B)

I circular

II linear

(C)

I linear

II wavelike

(D)

I wavelike

II linear

The given figure shows a girl playing in an amusement park. She is swinging on a swing.

The given statement is correctly completed by row

I (A) per iodic

II linear

(B)

I wave

II circular

(C)

I periodic

II wave

The type of motion described by the girl on the swing is

(D)

I circular

II linear

(A) Linear (C) Periodic

(B) Circular (D) Random

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6th Class Physics

18

6.

The motion of a top is an example of

11.

motion, whereas that of the bob of

a pendulum is an example of

motion.

The information in which alternative completes the given statement?

7.

8.

9.

(A)

i periodic

ii rectilinear

(B)

i rectilinear

ii circular

(C)

i periodic

ii rotational

(D)

i rotational

ii periodic

12.

In order to push or pull an object (A) Force must be applied (B) Speed must be applied (C) Friction must be applied (D) Electricity must be applied Roger noticed a book lying on a table . In order to move the book, he must apply a (A) Gear (B) Load (C) Force (D) Speed A wheelchair is pushed from West to East, as shown in the given figure. After traveling some distance, it takes two left turns. Finally, it takes a right turn and comes to a halt. Before the wheelchair comes to a halt, the direction of force on it is from: Push

North East

West

13.

A large box, placed on the ground, has to be shifted up to a wall, as shown in the given figure. Three boys push the box together. They have to apply a large amount of force to move the box. The motion of the box is opposed by the frictional force between the box and the ground.

If wheels were present below the box, then they would have to apply (A) More force (B) Same force (C) Less force (D) No force In a game of tug-of-war, Mark pulls the rope with a force of 60 N from the right. Sandy and George pull the rope with respective forces of 40 N and 20 N from the left. The net force on the rope is

(A) 0 N (B) 2 N (C) 60 N (D) 120 N Four boys, Hunter, Jackson, Samuel and Sean are pushing a heavy box. Their respective forces are listed below. Boy Force (N) Hunter 25 Jackson 25 Samuel 30 Sean 35 As a result of the presence of sand on the ground, the frictional force between the box and the ground is 15 N. The total force experienced by the box is

South

10.

(A) West to East (B) East to West (C) North to South (D) South to North A car moves with a constant speed toward East. A force is applied on the car to make it stop. The direction of the applied force is toward (A) North (B) South (C) West (D) East

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Hunter Jackson Samuel Sean

(A) 100 N toward the left (B) 115 N toward the left (C) 100 N toward the right (D) 115 N toward the right

Motion & Force

19

A bicycle possesses more than one type of motion.

forth about a fixed point. The information in which alternative completes the given statement?

The pedal of a bicycle has

(A)

i rectilinear

ii circular

(B)

i circular

ii periodic

HOTS Worksheet 1.

while its wheels have

of motion, of motions.

The information in which alternative completes the given statement?

i only one type

ii two types

(C)

i periodic

ii rectilinear

(B)

i two types

ii only one type

(D)

i circular

ii rectilinear

(C)

i two types

ii three types

(D)

i only one type

ii three types

(A)

2.

During an exhibition, four objects having different motions are displayed. The objects and their motions are shown in the given figure.

5.

6.

7.

3.

4.

Which of the given objects has circular motion? (A) Seesaw (B) Pendulum (C) Fan blades (D) Drum sticks Which of the following objects does not have more than one type of motion? (A) Motion of a leaf (B) Motion of a screw (C) Motion of a car’s wheel (D) Motion of a rolling coin In 

motion, the distance of an object from

a fixed point remains constant, while in 

8.

Which of the following motions is rectilinear motion? (A) Motion of a swing (B) Motion of the skin of a drum (C) Motion of a marching soldier (D) Motion of the hour hand of a clock Four types of motion, which are caused by the action of direct and indirect forces, are described in the table. Fluttering of a flag because of I wind II

Falling of a ball on the ground

III

Dropping of an apple from a tree

IV Falling of water from a bottle Which of the four types of motion is caused by the application of a direct force? (A) I (B) II (C) III (D) IV When a wooden box is suspended by a spring balance, the spring stretches because (A) Earth’s gravity pulls the box (B) Earth’s magnetic field attracts the spring (C) of the frictional force between the box and the spring (D) of the electrostatic force between the box and the spring Joanna is playing carrom along with her friends. She strikes the striker with her index finger and pockets the queen. Joanna uses which force for pocketing the queen? (A) Electric (B) Magnetic (C) Muscular (D) Gravitational

motion, an object moves back and www.betoppers.com

6th Class Physics

20 9.

Some magnets are brought in contact with a refrigerator. The magnets stick to the refrigerator because of (A) Gravitational force (C) Electric force

10.

14.

Earth revolves around Sun in 365 days. Earth and Sun are not in contact with each other. Earth’s revolution around Sun is caused by the

(B) Magnetic force (D) Nuclear force

(A) Shape of Sun (B) Shape of Earth

A small bar magnet is held by the magnetic force of a strong bar magnet fixed on its position on a rough inclined plane, as shown in the given figure.

(C) Force between Earth and Sun (D) Distance between Earth and Sun 15.

Gravitational force is

 force,  while 

force is repulsive as well as attractive. The given statement is correctly completed by row

(A)

The small bar magnet experiences (A) Only magnetic force (B) Magnetic and frictional forces

(B)

(C) Gravitational and magnet forces (D) Gravitational, magnetic and frictional forces 11.

Two magnets are placed at a distance from each other on a frictionless surface, as shown in the given figure.

(C)

(D) The magnets will experience (A) only magnetic force (B) only frictional force

A ball that is thrown up returns to the surface of Earth because of (A) Gravity (C) Electricity

13.

II

An attractive

Frictional

I

II

A repulsive

Magnetic

I

II

An attractive

Magnetic

I

II

A repulsive

Frictional

IIT JEE Worksheet

(C) magnetic and frictional forces (D) magnetic and gravitational forces 12.

I

I.

Single Correct Answer Type

1.

William lifts a load by pulling the rope of a pulley system. Which force is applied by William to lift the load?

(B) Friction (D) Magnetism

The direction of force on an upward moving ball is from

2.

(A) Magnetic

(B) Muscular

(C) Electrostatic

(D) Gravitational

Four situations I.  A boy throws a ball up in the air and it falls freely on the ground.

Earth

S UN

II. A horse pulls a cart and the cart moves forward. III.A can is opened with the help of an opener.

(A) Up to down (C) Left to right

(B) Down to up (D) Right to left

IV. A magnet is demagnetized by hammering it. In which of the given situations is indirect application of force involved? (A) I

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(B) II

(C) III

(D) IV

Motion & Force 3.

When a magnet is brought near another magnet, the second magnet moves toward the first. The second magnet moves because of  force between them which acts . (A)

(B)

(C)

(D)

4.

5.

6.

7.

8.

21

i

ii

Gravitational

Direct ly

i

ii

Gravitational

Indirectly

i

ii

Magnetic

Directly

i

ii

Magnetic

Indirectly

At an amusement park, a capsule in a free fall tower ride has a huge magnet fitted to its base. The capsule is prevented from hitting the ground by a powerful magnet, placed at the bottom of the ride. The magnet that faces upward has the same pole as the magnet that faces downward. Which force prevents the capsule from hitting the ground? (A) Gravitational (B) Magnetic (C) Electric (D) Nuclear Trenton is pulling a bucket full of water, out of a well. What is Trenton working against? (A) Gravitational pull of Earth (B) Magnetic field of Earth (C) Elasticity of the rope (D) Tension in the rope The wheel of a sewing machine describe (A) Translatory Motion (B) Periodic Motion (C) Circular Motion (D) None Which of the following decribe circular motion? (A) Motion of a merry-go- round. (B) Motion of an electric fan. (C) Motion of a spinning top. (D) All The motion of a girl swinging is (A) Translatory (B) Oscillatory (C) Circular (D) Random

9.

10.

The motion of a snake is (A) Translatory (B) Oscillatory (C) Circular (D) Random When you pluck a string of a guitar or sitar, it produces music. This is due to (A) Translatory motion of the strings (B) Vibratory motion of the string (C) Oscillatory motion of the string (D) Circular motion of the string

II.

Multiple Correct Answer Type

11.

Which of the following are examples for periodic motion? (A) The motion of the earth round the sun is periodic. (B) The swinging pendulum of a wall clock. (C) The needle of a sewing machine running at constant speed. (D) A car moving on a straight road. Which of the following describe random motion? (A) A buzzing bee. (B) A football player on the field. (C) A car moving on a circular road. (D) The flying motion of a sparrow. Which of the following is an effect of force? (A) Moving a body at rest. (B) Stopping a ball in motion. (C) Changing the direction of motion. (D) Changing the speed of a body in motion. Contact forces are (A) Magnetic force (B) Frictional force (C) Gravitational force (D) Muscular force Non contact forces are (A) Magnetic force (B) Frictional force (C) Gravitational force (D) Gravitational force

12.

13.

14.

15.

III.

16.

Paragraph Type The actual length covered by a moving body in between two points, irrespective of the direction in which the body is moving, is called distance. Displacement is the shortest distance between two points. The units of both distance and displacement are metre and centimeter. Using the above information answer the following quesitons. If a body completes one complete revolution in a circular path, then (A) distance = 0 (B) magnitude of displacement = 0 (C) Both (A) and (B) are correct (D) None of these www.betoppers.com

6th Class Physics

22 17.

18. 19.

A man leaves his house at 5.00 a.m. for a morning walk for 2km and returns at 6.00. a.m. What is his displacement traversed by him in this time? (A) 4 km (B) 8 km (C) 2 km (D) Zero In the above question, what is the distance travelled by the man? (A) 4 km (B) 8km (C) 2 km (D) Zero The figure given below shows the path taken by a boy during a walk. Find the total distance covered by the boy. B

4 km

3 km

2 km C

D

A

(A) 12 km (B) 9 km

(C) 10 km (D) 5 km

IV.

Matrix Matching (Match the following)

20.

Column – I (A) A car moving on a straight road (B) A javelin thrown by an athlete (C) Motion of a potter’s wheel (D) Motion of heart beats

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Column – II (p) Periodic motion (q) Rotatory motion (r) Curvilinear motion (t) Translatory motion

By the end of this chapter, you will understand     

Introduction to work Factors determining work Kinds of work Potential Energy Kinetic Energy

 Other forms of energy  Inter-conversion of energy  The Ultimate source of energy

Chapter - 3

Energy and Work

Learning Outcomes

1. Introduction The terms energy and work are commonly used in everyday life. For example, when we play and get tired we say we are left with very little energy. When we do a lot of home work, we say we are left with very little energy. After all, what is this energy?

A man pushing a car

Ability to do work is called energy. Now, the question arises, what is work? When you are preparing your lessons you may say you are doing mental work. When the headmaster of your school addresses the school assembly, he is doing mental work.

A speeding car

When a boy kicks a football, he is doing physical work. When a porter carries a load for you, he is doing physical work. When a car or a bus moves, it does mechanical work. You can see that work can be done by living or non-living bodies. However, we recognise only that work which causes some kind of motion or displacement. For example, if you are pushing a wall and it does not move, then no work is done. However, if you are pushing or pulling a chair such that it moves, then work is said to be done. When a force causes displacement in its own direction, work is said to be done. For example, if you are carrying your school bag on your back and standing, you are not doing any work. It is because the force applied by you is not making the bag move in its own direction. Similarly, if you push a wall and it does not move, then no work is done, no matter how much energy you have spent. On the other hand, if you apply force on a heavy box and it moves, then work is done. Similarly, when a cart man or the bullocks pull a cart, such that the cart moves, work is said to be done.

A boy preparing his lesson A wind mill moving with the force of air

6th Class Physics

24

(c) NOTE: For doing the work, two conditions are necessary: (i) A woman drawing water from a well

In some cases, the force applied does not produce displacement of a body. Instead the body gets deformed. For example, when an inflated rubber balloon is squeezed, it gets deformed in the direction of applied force. Thus, work is done.

(ii) The body must move in the direction of applied force. Mathematically, work is defined as the product of force and displacement through which force acts. If F is the applied force, ‘S’ is the displacement in the direction of applied force and W is the work done, then:

2. Factors Determining Work Consider an empty box being pushed from, position A to position B through a distance x. naturally, some force is required to move the box through distance x, and hence, some work is done. Now imagine that the box is filled with stones and it is again moved from A to B, through a distance ‘x’. It is obvious that the force required to do so will be more than that in the first case. In other words, more work is done in the later case. We can say that the work done by a body depends upon the force applied, i.e., the more the work done, the more is the force applied. Consider a box filled with stones. Let the box be displaced by 2 m from A to B by some force. Some work is done in moving the box. If the same force is used to push the box so that displacement is 4 m, the work done will be doubled. Thus, we can conclude that more the displacement of a body, more is the work done.

There must be force acting on the body.

Work done = Force × Displacement through which force acts. W=F×S Units of Work The unit of work in C.G.S. system is ‘erg’. W = F . S = 1dyne × 1cm = 1erg (i)

erg : Work done is said to be one ‘erg’ if a force of one dyne displaces the body through a distance of 1 cm along the direction of force. 1 erg = 1 dyne × 1 cm = 1 g cm s–2 × cm or

1 erg = 1 g cm2 s–2

The unit of work in S.I. system is joule (J) W = F . S = 1N × 1m = 1 joule (ii) Joule : Work is said to be one joule, if a force 1 newton displaces a body through a distance of 1 m along the direction of force. 1 J = 1 N × 1 m = 1 kg × m× s-2 × m 1 J = 1 kg m2 s–2

(a)

Relation between Joule and erg : 1 J = 1 N × 1 m = 105 dyne × 100 cm = 107 dyne cm or

(b) www.betoppers.com

1 J = 107 erg.

Work done can be positive, negative or zero depending upon the direction of force and direction of motion. (Displacement)

Energy and Work

25

Types of Work (i) Positive work done : Work done by a force on a body (or an object) is said to be positive work done when the body is displaced in the direction of applied force.

g = -ve

s=h

F

Vertically projected body S

Here

Negative work done

 Force  displacement are in the same direction Examples : (a) The body falling freely under the action of gravity has positive work done by the gravitational force. (b) The work done by the engine is positive. body

g = +ve

S=h

F S

u=0

Freely falling body

(ii) Negative work done : The work done by a force on a body is said to be negative work done when the body is displaced in a direction opposite to the direction of the force.

 displacem ent  force are in opposite direction. (a) When an object is lifted upward to a certain height, then the work done by the force of gravity (equal to the weight of the object) on the object is negative. (b) Work done by a person with a suitcase on his head moving upwards in the vertical direction. Here the displacement is in the upward direction and the force of gravity acts in the downward direction. (c) When brakes are applied on a moving vehicle, work done by the braking force is negative.

(iii) Zero work : a) If S = 0 i.e., the body does not move from its position on the application of force, then W=0 Thus, no work is done by the force if it fails to displace the body. b) When a person pushes a wall but fails to move the wall, then work done by the force on the wall is zero. c) When a body moves in a direction perpendicular to the direction of the force no work is done by the force. d) When a person carrying a suitcase in his hand or on his head is walking horizontally, the work done against gravity is zero. e) No work is done on a body when it moves along a circular path. f) Work done by the flying aeroplane is zero as the force and displacement are perpendicular to each other. Note: Work done is zero if 1. the displacement is zero. 2. the force and the displacement are perpendicular to each other.

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6th Class Physics

26 2.  S

 F

3. 4. 5.

6.

7.

Formative Worksheet 1.

2.

3.

4.

5.

Calculate the amount of work done, when a force of 25N displaces a body through 10m, in its own its direction. (A) 125 J (B) 250 J (C) 375 J (D) 500 J Renatta Gass is out with her friends. Misfortune occurs and Renatta and her friends find themselves getting a workout. They apply a cumulative force of 1080 N to push the car 218 m to the nearest fuel station. Determine the work done on the car. (A) 2.35 × 105 J (B) 2.35 × 106 J 7 (C) 2.35 × 10  J (D) 2.35 × 108 J A fork lift moves 34m carrying a 1023N box across the warehouse floor. How much work is done by the fork lift. (A) 3478 J (B)78234 J (C) 435720 J (D) 34782 J How much work is done by a person who uses a force of 27.5N to move a grocery buggy 12.3m? (A) 1014.75J (B) 676.5 J (C) 338.25 J (D) 169.125J 55, 000J of work is done to move a rock 25m. How much force was applied? (A) 1100 N (B) 2200 N (C) 3300 N (D) 4400 N

The factors on which work depends is (A) Force (B) Displacement (C) Both (D) None The CGS unit of work is (A) erg (B) joule (C) watt (D) metre The SI unit of work is (A) erg (B) joule (C) watt (D) metre What is the work done by a coolie of mass 80 kg, standing with a rice bag of 50kg on his shoulder? (A) 130 J (B) 50 J (C) 80 J (D) Zero Calculate the amount of work done when moving a 567N crate a distance of 20 meters. (A) 10340 J (B) 11340 J (C) 12340 J (D) 13440 J If it took a bulldozer 567.6 joules of work to push a mound of dirt 30.5 meters, how much force did the bulldozer have to apply? (A) 9.3 N (B) 10.6N (C) 18.6 N (D) 37.2 N

3. Kinds of Energy As already stated, the ability to do work is called energy. Thus, from the point of view of Physics if a body has energy, it must be able to cause motion and must exert some force. No doubt, there are many kinds of energy, but broadly speaking energy has been divided into two kinds, i.e., kinetic energy and potential energy.

4. Potential Energy Potential energy is a kind of stored energy in a body. Following investigations will prove the above statement. Let’s perform an activity. ACTIVITY-1 Suspend a brass bob from an iron stand as shown by the position C. Place a matchbox very close to brass bob (see the figure given below). Now stretch the brass bob to position A which is at a higher level. Release the brass bob. It will be seen that as brass bob hits the matchbox, it shifts from position 1 to position 2.

FCormative WW orksheet onceptive orksheet 1.

The ability to do work is called (A) Power (B) Energy (C) Charge (D) None Raised brass stores energy

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Energy and Work

(i)

27

Repeat the experiment by raising the brass bob to position B. It is seen that matchbox shifts from position 1 to position 3.

Mathematically, potential energy is the product of weight of body and vertical distance through which a body is raised.

Following conclusions can be drawn from the above investigation:

Potential energy = Weight of a body × Distance through which a body is raised. P.E.= mgh.

The work done in raising the brass bob is stored in it in the form of energy.

{Where, mg = weight of body , g = acceleration due to gravity with a value of 9.8 m/s2 and h = distance through which body is raised.}

(ii) The more is the work done in raising the brass bob to higher level, the more is the energy stored in it.

Examples of Potential Energy (iii) The stored energy in the brass bob can exert force, and hence, makes the matchbox move. ACTIVITY-2 Take a spring made from a strong wire and fix it on a wooden board as shown in figure given below.

(i)

When we wind up the spring of an alarm clock, our muscular energy is stored in its spring. It is this energy which is slowly released and moves the hands of the clock.

Wound-up spring of alarm clock

Compressed spring and an iron weight

(ii) In a toy pistol, the spring gets compressed and stores muscular energy. It is this stored potential energy which pushes out the plastic dart.

On the spring, place a 100 g weight or a stone and compress spring with your hand. You will notice that the shape or configuration of the spring changes. Remove the compressing force (your hand). It is seen that iron weight flies off.

(i)

From the above investigation, we conclude that Toy pistol energy can be stored in a body due to the change (iii) When the rubber sling of a catapult is stretched, in its configuration or shape. the muscular energy is stored in rubber in the form of potential energy. It is this stored potential energy From activities 1 and 2, it is clear that the energy which throws the stone in the sling of thecatapult which can be stored in a body depends upon: in forward direction. change in positions of body, i.e., how high the body is raised from ground level,

(ii) change in the configuration or shape of the body. This stored energy is called potential energy. The energy possessed by a body due to its position or configuration is called potential energy. catapult

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6th Class Physics

28 (iv) When the string of a bow is stretched, the muscular energy is stored in the string and bow in the form of potential energy. It is this potential energy which makes the arrow shoot forward.

From the above activity, following conclusions can be drawn Stretched bow and arow

Similarly, water stored high up in the dams; in water tanks on the top of the buildings has potential energy. When a blacksmith lifts a hammer high above his head or a woodcutter lifts an axe above his head, it is their muscular energy which is stored in the hammer or axe in the form of potential energy.

5. Kinetic Energy

(i)

A moving body has energy.

(ii) The energy of the moving body is more, if its mass increases. ACTIVITY-4 Place a wooden coin on the carrom board and hit it with a striker gently as shown in figure-a. It is seen that wooden coin moves forward through a small distance.

The bodies in motion are capable of doing work, and hence, possess energy. This energy is called kinetic energy. The word kinetic comes from Greek word Kineses which means motion. The energy possessed by a body due to its motion is called kinetic energy. ACTIVITY-3 Take two wooden boards. Incline one of the boards against the other board as shown in figure given below. At base of the inclined board place a glass marble B. On the top of the inclined board place a small marble A. Allow the marble A to roll down the inclined plane, so that it hits marble B. Measure the distance through which marble B moves. Repeat the experiment with a bigger marble C. Measure the distance through which marble B moves. It is seen that in the second case marble B moves through a larger distance.

Repeat the process, but hit the striker with full force. It is seen that wooden coin moves through a large distance. It even strikes the edge of board and moves in other direction. www.betoppers.com

Energy and Work

29

From this investigation, we can conclude that the more the speed of moving body, the more is its kinetic energy. Factors Determining Kinetic Energy From activities 3 and 4, it is clear that kinetic energy of a body depends upon following factors: (i) The more the mass of a body, the more is its kinetic energy. (ii) The more the speed of a moving body, the more is its kinetic energy. In higher classes, you will learn that:

(d) Hurricane blowing off roof of a hut

1 Kinetic energy= × Mass of the body × (Speed)2 2

K.E. =

1 × m × v2 2

Examples of Kinetic Energy Any material object which moves has kinetic energy. For example (i)

A running train has kinetic energy.

(ii) A speeding car has kinetic energy.

(e) Shooting arrow

(a) A running train (f) Stone rolling down the slope of hill

(b) A speed car

Freely oscillating pendulum (c) Strong wind

(iii) A strong wind, blowing off the leaves from a tree, has kinetic energy. (iv) Hurricane blowing off the roofs of huts, has kinetic energy. www.betoppers.com

6th Class Physics

30 (v) A shooting arrow has kinetic energy.

8.

(vi) A stone rolling down a hill has kinetic energy. Inter-conversion of Kinetic Energy into Potential Energy

9.

Suspend a brass bob from some support with the help of 1 strong cotton thread. This arrangement forms a pendulum. Pull the pendulum to position A. In doing so, we have raised the pendulum, and hence, our muscular energy is stored in it in the form of potential energy. Now release the pendulum. As the pendulum moves from position A to B, its speed goes on increasing and height goes on decreasing. Thus, we can say the potential energy at A changes into kinetic energy, till at B all the potential energy changes into kinetic energy. When the pendulum moves from position B to position C, it gains height and at the same time slows down. Thus, from B to C its kinetic energy changes into potential energy. At C, the pendulum will have maximum potential energy. During reverse motion, i.e., from C to B, the potential energy changes into kinetic energy. Similarly, from B to A, the kinetic energy changes into potential energy. Thus, we conclude that potential energy and kinetic energy  are  inter­convertible. As  all  the  forms  of energy can be put under the heading of either potential energy or kinetic energy, we reach to a point where we can define a law called law of conservation of energy. Law Conservation of Energy The sum total of energy in a system is a constant quantity. It can neither be created nor destroyed. However, energy can change from one form to another form.

Formative Worksheet 6.

7.

A person of mass 50 kg climbs a tower of height 72 metre. The work done is [g = 9.8 m/s2] (A) 35280 J (B) 32580 J (C) 52380 (D) 58320 J How much is the mass of a man if he has to do 2500 joule of work in climbing a tree 5m tall ? (g = 10 m/s2) (A) 30 kg (B) 40 kg (C) 50 kg (D) 45 kg

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10.

11.

12.

13.

14.

15.

An object of 100 kg is lifted to a height of 10 m vertically. What will be the work done? [g = 9.8 m/ s2 ] (A) 9800 J(B) 9008 J (C) 9.8 J (D) 8.9 J A box of mass 2 kg is pushed along a floor through 2m against a force of friction 5N. The same box is lifted up through a height of 2m. What will be the work done in both cases respectively (g = 9.8 m/ s2 ) (A) 10 J, 39.2 J (B) 15 J, 36.2 J (C) 12 J, 39.2 J (D) 10 J, 32.9 J A coolie lifts a box of 15 kg from the ground to a height of 2.0 m. The work done by the coolie on the box is ( Given g = 9.8 m/s2) (A) 250 J (B) 294 J (C) 300 J (D) 350 J A work of 4900 J is done on a load of mass 50 kg to lift it to a certain height. What is the height through which the load is lifted ? (A) 12 m (B) 14 m (C) 10 m (D) 18 m What will be the K.E of a body of mass 2 kg moving with a velocity of 0.1 metre per second ? (A) 0.1 J (B) 0.01 J (C) 0.001 J (D) 1 J Two bodies of equal masses move with uniform velocities v and 3v respectively. Find the ratio of their kinetic energies. (A) 9 :1 (B) 2 : 9 (C) 1 : 9 (D) 1 : 1 A 1kg mass has a kinetic energy of 1 Joule when its velocity is (A) 0.45 m/s (B) 1 m/s (C) 1.4 m/s (D) 4.4 m/s An object of mass 1 kg has a potential energy of 1 J relative to the ground, when it is at a height of [g=10 m/s2] (A) 0.1 m (B) 1 m (C) 9.8 m (D) 32 m

FCormative WW orksheet onceptive orksheet 8.

9.

When a body rolls down an inclined plane, it has (A) only kinetic energy (B) only potential energy (C) both kinetic and potential energy (D) neither kinetic energy nor potential energy The kinetic energy of a body depends (A) on its mass only (B) on its velocity only (C) on its mass as well as on its velocity (D) neither on its mass nor on its velocity

Energy and Work 10. Water stored at a height in a dam possesses (A) only kinetic energy (B) only potential energy (C) both kinetic and potential energy (D) neither kinetic energy nor potential energy 11. Strong wind can turn the blades of a wind mill because it possesses (A) kinetic energy (B) potential energy (C) both kinetic and potential energy (D) none of these 12. When the speed of a moving object is doubled, its (A) kinetic energy halved (B) kinetic energy decreases (C) kinetic energy is doubled (D) kinetic energy increases four times 13. A flying aeroplane has (A) only kinetic energy (B) only potential energy (C) both kinetic and potential energy (D) none of these 14. If the velocity an object increases 4 times, its kinetic energy increases (A) 4 times (B) 8 times (C) 16 times (D) 32 times 15. If a spring is compressed. The potential energy of the spring (A) remains unchanged (B) increases (C) decreases (D) becomes zero 16. A body of mass 1 kg is lifted through a height of 1m, then its work done is (A) 8.9 J (B) 9.8 J (C) 98 J (D) 89 J 17. A man lifts a brick of mass 5 kg from the floor to a shelf 2m high. How much work is done ? (g = 9.8 m/s2 ) (A) 8.9 J (B) 9.8 J (C) 98 J (D) 89 J 18. A ball of mass 1 kg is thrown up. It reaches a maximum height of 5m. What is the work done by the force of gravity during motion [g = 9.8 m/s2] (A) (D).9 J (B) 6.9 J (C) 49 J (D) 9.8 J 19. A load of 100 kg is pulled upwards by 5m. Calculate the work done. [g = 9.8 m/s2] (A) 4900 J(B) 9400 J (C) 9.(D) J (D) 94.0 J 20. If acceleration due to gravity is 10 m/s2, what will be the potential energy of a body of mass 1 kg kept at a height of 5 m ? (A) 20 J (B) 30 J (C) 40 J (D) 50 J

31

6. Other Forms of Energy No doubt energy can be classified either under the heading of kinetic energy or potential energy. “Yet for the sake of convenience, we have classified energy under different headings. 1.

Mechanical Energy With exception of energy in fuels (such as kerosene oil, coal, etc., or the energy in cells and battery), all forms of kinetic energy and potential energy taken together, form mechanical energy. Muscular energy of all kinds of animals is also a kind of mechanical energy. In generating this energy, chemical energy of the food is utilized. It is released in the form of heat energy.

2.

Heat Energy or Thermal energy When you cook food in pressure cooker by placing it over stove, the heat energy changes water to steam. The steam, in turn, lifts the weight on the top of lid and whistles. This lifting of weight suggests that heat is a form of energy which is capable of doing work.

In 1765, James Watt, a young scientist, noted this phenomenon which led to invention of steam engine. In the modern thermoelectric power houses, it is the heat energy of burning coal which is used to raise steam. The steam then runs the turbines of the generator and produces electric energy.

Diesel railway engine

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6th Class Physics

32

3.

4.

5.

All modern automobiles need heat energy. Whether it is a moped or a heavy truck or diesel railway engine, all use heat energy of burning petrol or diesel for doing work. We ourselves are dependent on heat energy’ for doing work. The food which we consume burns slowly in our cells to liberate heat energy. It is this heat energy which makes us do muscular work. Light Energy Light does not seem to move objects, as it is a very weak kind of energy. However, if a very intense beam of light is allowed to fall on fine dust particles, they are found to move. This suggests that light is a form of energy which is capable of doing work. Sound Energy Sound does not seem to move objects, as it is a fairly weak kind of energy. However, when the sound waves fall on the ear-drum, they make it vibrate. It is these vibrations which are carried to the brain and we hear sound. Thus, sound is a form of energy which is capable of doing work. When a supersonic plane breaks the sound barrier, the sound waves produced by it, really shake the buildings. Similarly, the thunder of the cloud also shakes buildings, thereby suggesting that sound is an energy. Electric Energy Electric energy is one of the most important forms of the energy for modern living. When this energy is passed through an electric motor, it sets its axle in circular motion. It is this circular motion, which is utilised in running ceiling fans; table fans; juicers; grinders; etc. It is used for running electric trains. It is used in factories for running heavy machines. It is also used in heating devices such as heaters, geysers, electric kettles, etc. It is also use of lighting in bulbs and tube lights.

Electric Kettle

6.

Electric grinder

Magnetic Energy A magnet can easily pull the pieces of iron towards itself. Thus, as a magnet is capable of causing motion in the iron articles, it has an energy which may be called magnetic energy. The figure (a) given below shows two trolleys A and B on which two powerful magnets are fixed, such that their North poles face each other. Bring the trolleys close to one another. You will notice that a lot of force is required to bring the trolleys close together.

(a)

(b) Now release the trolleys. You will observe that both the trolleys move away from each other as shown in figure (b). Thus, experiment proves that magnet has energy, which is commonly called magnetic energy. Magnetic energy is used in electromagnets to lift heavy loads of iron. It is also used in electric motors, electric generators, microphones, television tubes, telephones, etc. 7.

Electric train

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Chemical Energy The chemical energy is a kind of hidden energy in the atoms of elements or compounds. In fact, it is a kind of potential energy which is possessed by the atoms of elements or compounds on account of their arrangement of electrons. When these

Energy and Work

33

elements or compounds react, the arrangement of 7. electrons changes with the release of energy. This energy is, generally, released in the form of heat I. energy. For example, the food we eat, changes into (i) heat energy, because it is the chemical energy of food and the oxygen which changes into heat energy. Similarly, when we strike a match, the chemical energy on the match head changes into heat energy. In fact, it is the chemical energy of fossil fuels, such as coal or petroleum, which changes into heat energy when we use them. In special cases such as electric cells or electric batteries, chemical energy changes into electric energy. 8.

Inter-Conversion of Energy Inter-conversion of Mechanical Energy When an electric drill is used to bore a hole in a wooden block, smoke starts rising. It is because mechanical energy of drill changes into heat energy as shown in the figure given below.

Nuclear Energy The nucleus within the atom has enormous amount (ii) When two stones are struck against each other of energy which holds the protons and neutrons sharply, sparks of light are produced along with together. When the nucleus of a heavy atom such sound. Thus, mechanical energy changes into as uranium or plutonium is smashed, it releases light and sound energies as shown in the figure nuclear energy in the form of heat and light energy. given below. The nuclear energy can be used for peaceful purposes as well as destructive purposes.

Atomic explosion

Atom bomb and Hydrogen bomb are the devices in which nuclear energy is released suddenly. It causes enormous damage.

(iii) When the water stored in dams is allowed to flow from a pipe and directed against turbine, the mechanical energy of the flowing water rotates the turbine. The turbine is coupled to electric generator, where the mechanical energy of the turbine changes into electric energy as shown in the figure given below.

In nuclear power plants, nuclear energy is used for peaceful purposes. The heat energy released during nuclear reactors is used to raise steam. The steam is then used to run electric turbines to generate electric energy. 9.

Radiant Energy While vibrations of matter produce thermal and sound energy, radiant energy results from vibrations of charges. Radiant energy is another name for waves of electromagnetic energy. For example, the sun’s energy is transported to Earth as waves of radiant energy. Radio waves, microwaves, infrared radiation, light waves, X-rays and cosmic rays are all waves of radiant energy.

Hydro power plant

A spark generator converts mechanical energy of motion into the electrical energy of a spark. When the spark generator ’s spring is compressed, mechanical energy is stored as potential strain energy. When the stored strain energy is released, the spring exerts force on the surfaces of a certain www.betoppers.com

6th Class Physics

34 type of crystal, which then becomes electrically charged. If enough charge accumulates on the surfaces, a spark will jump between oppositely charged parts of the crystal. (iv) Mechanical energy of motion is converted into thermal energy when surfaces rub together, producing friction between the objects. We can illustrate thermal energy from friction by using an electric drill to rotate a metal tube filled with water. Two blocks of wood squeezed against the tube produce the friction. When we pour a small amount of water into the metal tube and cork it with a rubber stopper, the mechanical energy of motion converted into heat by friction turns the water into steam. The steam blows the cork out of the tube, thus converting thermal energy back into mechanical energy of motion of the stopper. II. Inter-conversion of Heat Energy (i)

In steam engines or diesel engines, the heat energy is converted into mechanical energy.

IV. Inter-conversion of Sound Energy When we speak in front of a microphone, the sound energy changes into electric energy (Fig.a). V.

Inter-conversion of Magnetic Energy

(i)

When an electric generator works, the mechanical energy interacts with magnetic energy and changes into electric energy.

(ii) If two magnets are placed on top of one another with their like poles facing, the magnets repel each other. We can feel this force when we do work to push the top, floating magnet closer to the bottom magnet. When we release the floating magnet, some magnetic energy is converted into mechanical energy of motion and gravitational potential energy as the magnet moves upward and floats. VI. Inter-conversion of Electric Energy (i)

In electric motors; fans; grinders; etc., the electric energy changes into mechanical energy.

(ii) Appliances, such as toasters and hair dryers, contain thermostats to regulate their temperature. Some thermostats illustrate the conversion of thermal energy into mechanical energy of motion. (ii) In the preparation of certain chemical compounds, the heat energy changes into chemical energy. III. Inter-conversion of Light Energy (i)

During photosynthesis, the light energy changes into chemical energy. The plants take the carbon dioxide gas and water and these react with the help of chlorophyll and sunlight to form starch and oxygen.

microphone

Electric Motor

(ii) When light energy falls on silver salts coated on photographic plate, it changes into chemical energy. (iii) When light energy is absorbed by photo-voltaic cells, it changes into electric energy Photo-voltaic cells are commonly used in electronic calculators; wrist watches; photographic cameras; etc.

Electric fan

(ii) In electric kettles and electric room heaters, the electric energy changes into heat energy. (iii) In electric bulbs, tube lights, etc., the electric energy first changes into heat energy and then light energy. (iv) In electromagnets, the electric energy changes into magnetic energy.

A calculator

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Electronic Wrist watch

(v) During the electrolysis of salt solutions the electric energy changes into chemical energy.

Energy and Work

35

VI. Inter-conversion of chemical Energy (i)

During the process of burning, the chemical energy changes into heat energy and light energy. When wood is burnt, the chemical energy changes into heat and light energies.

(ii) In electric dry cells or car batteries, the chemical energy changes into electric energy.

flowing water is made to run the turbine, which is coupled to an electric generator. In the electric generator, the kinetic energy of rotating turbine is converted into electric energy. The electric energy is carried over long distances through the copper wires mounted on the transmission towers. In a way any kind of energy which we use on earth has come from the sun in the form of solar energy.

car battery

(iii) In explosive devices, such as fire crackers, bombs, etc., the chemical energy changes into heat, light and sound energies.

8. All Energy Chains Start from the Sun The sun produces an enormous amount of heat energy and light energy due to fusion of hydrogen atoms. For us on the surface of the earth, the sun is the prime source of energy. The green plants absorb carbon dioxide from air and water from soil and then, with the help of chlorophyll and sunlight, convert them into starch and oxygen. Thus, the solar energy is trapped by the plants in the form of chemical energy. It is this chemical energy in the food which changes into heat energy and then muscular energy in our bodies. Even in the fossil fuels such as coal or petroleum (which are formed from the plants or animals), the chemical energy is basically the trapped solar energy. The water cycle is also caused due to solar energy. A large amount of water vaporises due to solar energy. When this water forms clouds and it rains, it is the solar energy which changes into mechanical energy of water.

Energy Chain

Solar energy is directly used by us in drying clothes and other materials. Solar energy is directly used in solar cells which are used in watches; calculators and artificial satellites. Solar cookers are used fori cooking food.

Artifical satellite

Flowing water is a very important source of energy. These days big dams are constructed on the rivers. The water stored in the dams has potential energy. When the stored water is made to flow through special channels, the potential energy of water changes into kinetic energy. The kinetic energy of www.betoppers.com

6th Class Physics

36

Formative Worksheet 16. Which of the following belongs to the category of mechanical energy? (A) Kinetic energy (B) Potential Energy (C) Muscular energy (D) All 17. When you cook food in pressure cooker by placing it over stove, the _____energy changes water to steam. (A) Electrical (B) Magnetic (C) Chemical (D) Heat 18. Who invented steam engine? (A) Joule (B) James Watt (C) Newton (D) Rutherford 19. Which energy causes the sensation of vision? (A) Sound (B) Electrical (C) Magnetic (D) Light 20. Which of the following is capable of doing work? (A) Sound energy (B) Light energy (C) Heat energy (D) All 21. Which energy makes an electric motor to work? (A) Sound energy (B) Light energy (C) Heat energy (D) Electrical energy 22. Chemical energy is kind of (A) Kinetic energy (B) Potential energy (C) Both (D) None 23. In fossil fuels, _____ energy changes to heat energy. (A) Sound energy (B) Chemical energy (C) Heat energy (D) Electrical energy 24. When the nucleus of a heavy atom such as uranium or plutonium is smashed, it releases (A) nuclear energy (B) heat energy (C) light energy (D) All 25. Which of the following is the result from vibration of charges? (A) Thermal energy (B) Sound energy (C) Radiant energy (D) Heat energy 26. In which of the following, mechanical energy is converted to heat energy (A) Drilling (B) Striking of stones (C) Water fall (D) None 27. When the turbine is coupled to an electric generator, ________ energy of the turbine changes into ________energy. (A) electric, mechanical (B) mechanical, electric (C) sound, light (D) electric, magnetic www.betoppers.com

28. In which of the following, heat energy is converted to mechanical energy? (A) Steam engines (B) Diesel engines (C) Petrol engines (D) All 29. When light energy falls on silver salts coated on photographic plate, it changes into ____ energy. (A) Electrical (B) Heat (C) Chemical (D) None 30. In which of the following light energy changes to electric energy? (A) Electronic calculator (B) Photographic cameras (C) Wrist watches (D) All 31. If two magnets are placed on top of one another with their like poles facing, the magnets repel each other. In this case, some magnetic energy is converted into ______. (A) Electric energy (B) Mechanical energy (C) Gravitational potential energy (D) Both B and C 32. In an electric kettle, ______ energy is changed ______ energy? (A) electric, magnetic (B) mechanical, electric (C) electric, heat (D) electric, light

Conceptive Worksheet 21. In generating muscular energy, ______ energy of food is utilized. (A) Electrical (B) Magnetic (C) Chemical (D) Heat 22. Heat is a form of _____ (A) Velocity (B) Power (C) Energy (D) Speed 23. Which energy makes us to do muscular work? (A) Electrical (B) Magnetic (C) Chemical (D) Heat 24. Which energy causes the sensation of hearing? (A) Sound (B) Electrical (C) Magnetic (D) Light 25. Which energy is released during thunder storm? (A) Sound energy (B) Light energy (C) Heat energy (D) All

Energy and Work 26. Which energy is hidden in atoms of elements or compounds? (A) Sound energy (B) Chemical energy (C) Heat energy (D) Electrical energy 27. When we strike a match, the ______energy on the match head changes into ______energy. (A) sound, chemical (B) chemical, light (C) chemical, heat (D) chemical, electrical 28. In electric cells or electric batteries, _______energy changes into _____energy. (A) sound, chemical (B) chemical, light (C) chemical, heat (D) chemical, electrical 29. During which of the following explosions, nuclear energy is released suddenly? (A) Hydrogen bomb (B) Atom bomb (C) Both (D) None 30. Which of the following are the waves of radiant energy? (A) Radio waves (B) Infrared (C) X rays (D) All 31. When two stones are struck against each other sharply, mechanical energy is converted to (A) Electrical energy (B) Light energy (C) Sound energy (D) Both B and C 32. When hands are rubbed, ________ energy is changes into ________energy. (A) electric, mechanical (B) mechanical, thermal (C) sound, light (D) electric, magnetic 33. During which of the following, light energy is converted to chemical energy? (A) Photosynthesis (B) Combustion (C) Respiration (D) All 34. In which of the following light energy changes to electric energy? (A) solar cooker (B) Pressure cooker (C) Wrist watches (D) All 35. In which of the following, sound energy changes into electric energy? (A) Electronic calculator(B) Photographic cameras (C) Wrist watches (D) Microphone 36. In which of the following, the electric energy changes into mechanical energy? (A) Electric motors (B) Fans (C) Grinders (D) All

37

Summative Worksheet I.

Fill in the blanks

1.

Ability to do work is called_________.

2.

When a force causes _____________in its own direction, the work is said to be done.

3.

Work done by a body is the product of ________ and displacement.

4.

One joule is the product of force of 1N and displacement of______.

5.

Energy possessed by a body by virtue of its configuration or________ is called potential energy.

6.

Energy possessed by a body by virtue of its ______________is called kinetic energy.

7.

In hydroelectric dams the _________energy of flowing water is transformed into electric energy.

8.

When we speak in front of a microphone, the sound energy changes into_____energy.

9.

Nuclear energy is released in the for m of ________________ energy when the atom disintegrates.

10. During photosynthesis, the ______energy changes to chemical energy. II. Statements given below are incorrect. Write the correct statements. 11. Work is done when we hold a pile of books in our hands. 12. Work done by a body is the product of pressure and displacement. 13. When electric current flows through a bulb, the electric energy first changes into light energy and then heat energy. 14. When we speak in front of a microphone the electric energy changes into sound energy. 15. During photosynthesis heat energy changes into chemical energy. 16. In charging a car battery, the chemical energy changes into electric energy. 17. A wound up spring of a watch possesses kinetic energy.

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6th Class Physics

38 18. Nuclear energy is released in the form of light energy.

34. Water stored in a tank on the top of roof has: (A) potential energy

19. When a stone is projected vertically upwards its kinetic energy changes into potential energy. 20. Kinetic energy of a body decreases with the increase in mass.

(C) potential as well as kinetic energy (D) solar energy 35. The ultimate source of energy on the earth is: (A) coal (C) flowing water

III.. State whether the following statements are true or false: 21. Magnetic energy is always attractive in nature.

(B) kinetic energy

(B) petroleum (D) sun.

36. The cause of water cycle in nature is:

22. The SI unit of energy is Joule.

(A) chemical energy

(B) nuclear energy

23. A stretched bow and arrow system has kinetic energy.

(C) solar energy

(D) potential energy.

25. During photosynthesis, the light energy changes into chemical energy.

(B) kinetic energy

26. An electric bulb converts electric energy into heat energy.

(D) none of these.

37. Strong current of water turns the blades of turbine because it possesses: 24. The energy possessed by an electric cell is chemical energy. (A) potential energy

(C) both potential and kinetic energy

27. The source of energy in a nuclear bomb is chemical 38. Work is said to be done when: energy. (A) force acts upon a body, but the body does not move 28. A freely falling stone possesses K. E and P.E. 29. In human body, the chemical energy of food changes into heat energy.

(B) force acts upon a body and moves it in the direction of force

30. In hydroelectric stations, the potential energy of flowing water changes into electric energy.

(C) force acts upon a body, but the body does not move in the direction of applied force

IV. Choose the correct answer

(D) none of these

31. The work done by a body is the product of force 39. It two boys push a table in opposite direction with equal force, then and: (A) work is said to done (B) no work is done (A) distance (B) speed (C) displacement 32. The SI unit of work is: (A) newton (C) joule

(C) double work is done (D) none of these.

(D) velocity.

(B) pascal

40. When  a person  speaks  in  front of  a  micro­phone, the sound energy is converted into: (A) loud sound energy (B) magnetic energy

(D) newton-metre.

33. Burning of paper is an example of conversion of: (A) chemical energy into heat energy (B) chemical energy into heat and light energy (C) chemical energy into light energy (D) heat energy into light energy

(C) chemical energy (D) electric energy. V.

Find the odd one out. Give a reason for your choice.

41. Water stored in a tank, wound up spring of watch, stretched spring, speeding train. 42. A shooting star, a flying bird, blowing wind, a stone lying on the top of roof. 43. Coal, kerosene oil, petrol, solar cell.

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Energy and Work

39 6.

HOTS Worksheet 1.

(B) Distance

(C)  Energy 2.

3.

I A force must act on a body. II The body must be displaced. III Directions  of  the  applied  force  and the displacement must be the same.

Which of the following quantities is a vector quantity? (A) Displacement

(D) Work

With reference to the scientific definition of work done.

When brake is applied on moving car, its motion is retarded. In such a case, the work done by the brake on the car is said to be

(A) only II is inessential

(A)  zero

(B)  positive

(B) only III is inessential

(C)  negative

D)  positive or negative

(C) both I and II are  inessential

Which of the following conditions is correct for nonzero work done? (A)  Force acting on the body is zero.

(D) both I and III are  inessential 7.

(B)  Displacement of the body is zero. (C) Displacement  of  body  is  perpendicular  to  the force. (D)  Displacement produced by force is in opposite direction to the force. 4.

Three essential criteria for something to qualify scientifically as work done:

50 J of work is done against the force of gravity in lifting a stone to a certain height. What will be the potential energy of the stone at that height? (A) 200 J (B) 100 J

8.

(C) 50 J

(D) 30 J

The ability of a body to do some work is known as: (A) force (B) energy (C) power  (D) momentum

A constant force is acting upon a particle that is 9. always perpendicular to the velocity of the particle. The motion of the particle takes place in a plane and it is known as uniform circular motion. Which of the following statements is correct for uniform circular motion? 10.

20 J of work is done against the force of gravity in lifting a stone to a certain height. What will be the potential energy of the stone at that height?

(A) Velocity of the particle is constant.

(A)  rate of work done by the body

(B)  Acceleration of the particle is constant.

(A)  200 J (B)  100 J

(C)  20 J

(D)  10 J 

Energy of a body is defined as the

(B)  amount of work done by the body

(C)  Kinetic energy of the particle is constant. (D)  Work  done  by  perpendicular  force  on  the particle is non-zero. 5.

(C)  ability to do some work by the body    (D)  rate of change of velocity of the body

A boy carries a 20 kg load from point C to A along 11. Which of the following statements is correct with the path CA as shown in the figure.What is the reference to the work-energy theorem? work done by the boy against the gravitational pull (A) The  sum  of  the  kinetic  energy  and  potential of the earth? energy of a body is the work done by the net force on the body. (B) The  difference  of  the  kinetic  energy  and potential energy of a body is the work done by the net force on the body. (C) The change in the potential energy of a body is the work done by the net force on the body. (D) The change in the kinetic  energy  of a body is the work done by the net force on the body. (A) 190 J (B) 289 J

(C) 392 J

(D) 490 J www.betoppers.com

6th Class Physics

40

12. Cars I and II, having masses m and 2m respectively, 16. Which of the following statements is correct for are moving with velocities hydro power plants? 2v and v respectively. They are brought to rest by (A)  Chemical  energy  is  converted  into  electrical the application of breaks. The cars take the same energy. time and cover the same distance before coming (B)  Electrical  energy   is  converted  into  chemical to rest. energy. What is the ratio of change in kinetic energy of car I to that of car II? (C)  Mechanical energy is converted into electrical energy. (A) 1 : 2 (B) 2 : 1 (C) 1 : 4 (D) 4 : 1 13. A car of mass 1200 kg starts from rest and acquires (D)  Electrical energy is converted into mechanical a uniform velocity of 18 m/s. What is the work energy. done on the car? 17. Which of the following materials is not a biomass (A) 184400 J (B) 188400 J fuel? (C) 194400 J (D) 198400 J (A) Wood (B) Crops 14. Which of the following statements is correct with (C) Plastic (D) Organic  garbage reference to the work-energy theorem? (A) The  sum  of  the  kinetic  energy  and  potential 18. The main reason for the production of ocean waves is the _____________. energy of a body is the work done by the net force on the body. Which information completes the given statement? (B) The  difference  of  the  kinetic  energy  and (A) gravitational pull of the sun potential energy of a body is the work (B) gravitational pull of the moon done by the net force on the body. (C) winds that blow across the earth (C) The change in the potential energy of a body is (D) winds that blow across the sea the work done by the net force on the body. (D) The change in the kinetic  energy  of a body is 19. Hydro power plants use _______ energy of water the work done by the net force on the body. accumulated at a height to spin a turbine. Which 15. A block of magnet is kept with its North-pole on the ‘form of energy’ completes the given statement? top and the South-pole at the bottom, as shown in (A) potential (B) chemical the given figure. (C) kinetic (D) heat Another special magnet of a relatively small size is dropped on top of the block magnet. It is observed that the two magnets do not come in contact with each other. Which diagram shows the exact positions of the poles on the special magnet?

(A)

(C)

(B)

(D)

20. Which arrow diagram correctly represents the steps in energy conversion in hydropower plants? (A) Heat  energy   Kinetic energy  Electric energy (B) Kinetic  energy   Heat energy  Electric energy (C) Kinetic energy   Potential energy  Electric energy (D) Potential energy   Kinetic energy  Electric energy 21. The energy produced by exploiting the differences in temperatures between the water on the surface and at the bottom of the ocean is harnessed in a (A) geothermal power  plant (B) wave  energy  power  plant (C) tidal energy power plant (D) ocean thermal  power plant

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Energy and Work 22. The strong winds that blow over the sea is useful in the generation of (A) tidal  energy (B) wave  energy C) geothermal  energy (D) ocean  thermal  energy 23. In which of the following solar devices the ultimate energy that is produced is not heat energy? (A) Solar cell (B) Solar  heater (C) Solar cooker (D) Solar  furnace 24. Which of the following statements about wind power plants is correct? (A)  It cannot be built along coastlines (B) It can be built only along coastlines (C) It cannot be built in regions with constant high wind speeds (D) It can be built only in regions with constant high wind speeds 25. Consider following statements. I. Biogas is a conventional source of energy.

41 3.

4.

A frontend loader needed to apply 137 newtons of force to lift a rock. A total of 223 joules of w o r k was done. How far was the rock lifted? (A) 1.627 m

(B) 2.6225 m

(C) 3.2564 m

(D) 4.2545 m

A young boy applied a force of 2,550 newtons on his St. Bernard dog who is sitting on the boy’s tennis shoes. He was unable to move the dog. How much work did he do trying to push the dog? (A) 10 J

5.

6.

(B) 20 J

IIT JEE Worksheet I. 1.

2.

7.

(D) none

What will be the velocity of a body of mass 100 g having a kinetic energy of 20 J ? (A) 20 m/s

(B) 15 m/s

(C) 10 m/s

(D) 25 m/s

The kinetic energy of an object of mass ‘m’ moving with a velocity of 5 m/s is 25 J. What will be its K.E when its velocity is increased three times ? (A) 225 J (B) 200 J

II. Biogas is formed in the absence of oxygen. III. Biogas can be stored before utilization. Among the given statements, (A) only  statement I is  correct (B) only  statement III is  correct (C) statements I and II are  correct (D) statements II and III are  correct

(C) 30 J

(C) 150 J

(D) 100 J

A car is moving with a uniform velocity of 54 km/h. What is the K.E of a boy of mass 40 kg sitting in his car? (A) 4500 J (B) 4000 J (C) 3500 J (D) 3000 J

8.

What will be the height through which a body of mass 0.5 kg should be lifted, if the energy spent for doing so is 1.0 joule ? (g = 10 m/s2) (A) 0.1 m (B) 2 m

(C) 1 m

(D) 0.2 m

9. During electrolysis, electrical energy is changed to Single Correct Answer Type ___ energy. You and 3 friends apply a combined force of 489.5N (A) Light (B) Sound to push a piano. The amount of work done is 1762.2J. What distance did the piano move? (C) Chemical (D) Gravitational (A) 3.6 m (B) 4.7 m (C) 5.8 m (D) 6.9 m 10. During burning, chemical energy is changed to If a weight lifter raises a barbell with a mass of _____ energy. 125.7 grams doing 5,023 joules of work, what (A) heat (B) light (C) both (D) none distance did he move the barbells? Remember that you need a force, not a mass. You must f i r s t 11. In which of the following, chemical energy is calculate the force in order to complete your changed to electrical energy? solution. HINT: Weight is a force. Weight on earth (A) Burning (B) dry cells is determined by multiplying an object’s mass times (C) electric kettle (D) Solar cooker earth’s gravitational pull (9.8m/s2 ). 12. In explosive devices, such as fire crackers, bombs, (A) 2032.2 m (B) 3253.6 m etc., the chemical energy changes into ____ (C) 4083.7 m (D) 5465.8 m energy? (A) heat (B) light

(C) sound

(D) All

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6th Class Physics

42 II. Multi Correct Answer Type

III. Paragraph Type

13. Choose the one fall under the category of mechanical I. energy. (A) Kinetic energy (B) Potential Energy (C) Muscular energy (D) Electrical Energy 14. Which of the following is a form of energy?

Mathematically, work is defined as the product of force and displacement through which force acts.If F is the applied force, ‘S’ is the displacement in the direction of applied force and W is the work done, then: Work done = Force × Displacement through which force acts.

(A) Sound

(B) Light

W=F×S

(C) Heat

(D) Momentum

The SI unit of work is Joule (J) and cgs unit is erg. 1 J = 107 erg.

15. When the nucleus of a heavy atom is smashed, it releases (A) nuclear energy (B) heat energy (C) electrical energy (D) light energy 16. Nuclear energy is released by the explosion of (A) Hydrogen bomb (C) Flower pot

(B) Atom bomb (D) Fire Cracker

17. The waves of radiant energy are (A) Radio waves

(B) Infrared

(C) X rays

(D) Cathode rays

18. Mechanical energy is converted to _____, when two stones are struck against each other sharply. (A) Electrical energy (B) Light energy (C) Sound energy

(D) Magnetic energy

19. Heat energy is converted to mechanical energy in (A) Steam engines

(B) Diesel engines

(C) Petrol engines

(D) Electric bell

20. Light energy changes to electric energy in (A) Electronic calculator(B) Photographic cameras (C) Solar Cooker

(D) Wrist watches

21. If two magnets are placed on top of one another with their like poles facing, the magnets repel each other. In this case, some magnetic energy is converted into ______. (A) Electric energy

(B) Mechanical energy

23. How much work is done by a person who uses a force of 50 N to move a grocery buggy 10 m? 24. 6000 J of work is done to move a rock 25m. How much force was applied? 25. You and your friends apply a combined force of 800 N to push a stone. The amount of work done is 3200 J. What distance did the stone move? II. According to law of conservation of energy. “Energy can neither be created nor be destroyed, but can be changed from one form to another form”. 26. The sound energy in a microphone changes into (A) chemical energy (B) mechanical energy (C) electrical energy

(D) magnetic energy

27. The electrical energy in an electromagnet changes into (A) light energy

(B) heat energy

(C) magnetic energy

(D) chemical energy

29. During charging of a battery, the electrical energy changes into (A) magnetic energy

(B) chemical energy

(C) mechanical energy (D) none of these III. Relation between kinetic energy and momentum Let us consider a body of mass ‘m’ having a velocity ‘v’ , then momentum of the body P = mass × velocity

(C) Gravitational potential energy (D) Sound energy

P=m×v  v

22. The electric energy changes into mechanical energy in (A) Electric motors (C) Grinders www.betoppers.com

--------- (1)

From definition, kinetic energy (K.E) of the body

(B) Fans (D) Microphone

P m

K.E =

1 mv 2 2

--------- (2)

Energy and Work

43

Now putting the value of (1) in (2) we have

K.E 

K.E. =

1 P m  2 m

2

35. Column-1

Column-II

(a) Work

(p) Metre

(b) Force

(q) Joule

(c) Displacement

(r) Metre/second2

(d) Acceleration due to gravity (s) Newton

1 P2 1 P2 P2 m 2   ----- (3) 2 m 2 m 2m

36. Column-1

Thus we can write

Column-II

(a) Electric drill

(p) Heat to Mechanical

P = 2m × K.E

(b) Steam engine

(q) Sound to Electrical

P

(c) Photosynthesis

(r) Mechanical to Heat

(d) Microphone

(s) Light to Chemical

2

2m  K.E

Thus momentum =

2  mass  kinetic energy

29. What will be the momentum of a body of mass 100 g having kinetic energy of 20 J?

37. Column-1

Column-II

(a) Electric Generator (p) Electric to Mechanical

(A) 2 kg m/s

(B) 4 kg m/s

(b) Electric Motor

(q) Heat to Mechanical

(C) 5 kg m/s

(D) 6 kg m/s

(c) Burning

(r) Magnetic to Electric

30. Two bodies of mass 1 kg and 4 kg possess equal momentum. The ratio of their kinetic energies is

(d) Hair dryer (s) Chemical to Heat V. Integer Type (A) 4 : 1 (B) 1 : 4 (C) 2 : 1 (D) 1 : 2 38. How much work in Joule is done by a force of 4 N 31. Two bodies masses 1 kg and 4kg having equal kinetic is moving a body through a distance of 2 m in its energies. The ratio of their momentum is own direction ? (A) 4 : 1 (B) 1 : 4 (C) 2 : 1 (D) 1 : 2 39. The work done in pulling a load of 100 kg 4900 J. 32. Two bodies A and B of unequal masses having same momentum have masses in the ratio 1 : 2 then their K.E are in the ratio (A) 2 : 1 (B) 1 : 2

(C) 4 : 1

(D) 1 : 4

What is the height in metres to which it is pulled ? [g = 9.8 m/s2] 40. When mass and velocity and doubled, the kinetic energy becomes _____ times the original.

33. The kinetic energy of a given body is doubled. Its momentum will (A) remain unchanged (B) redoubled (C) become

1 times 2

(D) become

2 times

IV. Matrix Match Type Column-1

34.

Column-II

W F

(a) Work

(p)

(b) Kinetic energy

(q) mgh

(c) Potential energy

(r)

(d) Displacement

(s) F  S

1 2 mv 2

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44

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6th Class Physics

B y t h e en d o f t h i s ch a p t e r, y o u w i l l u n d er s t a n d    

Terms related to light Rectilinear propagation of light Pin hole camera Reflection of light

   

General terms to the refelction Laws of reflection Image Shadows

1. Introduction If we enter a dark room, objects present there are not visible. However, if a bulb is switched on, everything in the room becomes visible. It shows that for vision the presence of light is essential. Definition of Light: It is an invisible energy which causes in us sensation of sight (vision). Since light is obtained from heat energy, i.e., when an object is heated to a temperature beyond [500 0C, we can say that light is a kind of energy]. It must be kept in mind that light energy makes the surrounding objects visible, but by itself it is an invisible energy. Example: If we are seeing a coloured poster, then we are seeing only the poster and not the coloured lights reflected fronts it. It is because light is invisible. The various colours reflected from the poster excite the retina of the eye, which in turn sends a message to the brain. It is the brain which finally makes out the colours of the poster. Thus, we can conclude that light is an invisible energy which causes in us sensation of vision. Sources of Light: Sun is the primary source of light for mankind. In addition to it, lighted bulb, a fluorescent tube, a lighted candle ,a kerosene oil lamp, etc., are other sources of light. Speed of Light: Light travels at very fast speed i.e., 3 × 108 m/s. It means the speed of light is 300000000 m/s or 300000 km/s. Luminous Bodies: The bodies which give out light energy by themselves are called luminous bodies. Examples: The sun, the stars, glow worm etc. Non-luminous Bodies: The bodies which do not give light energy by themselves , but reflect the light energy falling on them are called non-luminous bodies. Examples: moon, wood, furniture etc.

Chapter - 4

Light

Learning Outcomes

2. Terms related to Light 1.

2.

3.

4.

5.

6.

7.

Optical Medium: Any material (or) nonmaterial through which light energy passes wholly (or) partially is called optical medium Examples: Vaccum, air, water, glass etc. Homogeneous Medium: An optical medium which has a uniform composition throughout is called homogeneous medium. Examples: Vaccum, diamond, distilled water, pure alcohol etc. Heterogeneous Medium: An optical medium, which has different composition at different points is called heterogeneous medium. Examples: Air, muddy water, fog, mist, clouds, smoke etc. Transparent Medium: A medium which allows most of the light energy to pass through it is called transparent medium. Examples: Vaccum , glass, clear air, alcohol, benzene etc. Translucent Medium: A medium which partially allows the light energy to pass through it is called translucent medium. Examples: oiled paper, tissue paper, ground glass, butter paper etc. Opaque Bodies: The bodies which do not allow the light energy to pass through them are called opaque bodies. Examples: Bricks, wood, metals etc. Point Source of Light: A source of light which is of the size of pinhead is called point source of light. Example: The pinhole act as a point source of light.

6th Class Physics

46 8.

9.

Extended Source of Light: Any source of light which is bigger than point source of light is called extended source of light Examples: Bulb, Tube light, burning candle etc. Ray of Light: The path along which light energy travels in a given direction is called ray of light.

Example: If a parallel beam is made to pass through a convex lens, then it meets at a point. This kind of collection of rays is called convergent beam of light.

Formative Worksheet 1.

10. Beam of Light: A collection of number of rays of light is called beam of light.

11. Parallel Beam: When the rays of light travels parallel to each other, then the collection of such rays is called parallel beam.

12. Divergent Beam: When the rays of light originating from a point ,travel in various directions, then the collection of such rays is called divergent beam.

2.

3.

Example: The rays coming out from a bulb or a burning candle or a car headlight constitute a divergent beam. Note: A point source produces a divergent beam of light. 13. Convergent Beam: When the rays of light coming from different directions, meet at a point then the collection of such rays is called convergent beam.

4.

5.

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Statement I :Diamond is a homogenous medium Statement II: Bodies which can absorb light energy are called opaque bodies (A) Both Statements are true, Statement - II is the correct explanation of Statement-I (B) Both Statements are true, Statement - II is not correct explanation of Statement - I. (C) Statement - I is true, Statement - II is false. (D) Statement - I is false, Statement - II is true. Match the following: Column-I Column-II (A) Optical medium 1) Vacuum (B) Heterogeneous medium 2) Muddy water (C) Transparent medium 3) Clear air (D) Translucent medium 4) Oiled paper 5) Fog Choose the correct statements: (A) Objects that allow light pass through them are called transparent objects (B) The objects which emit light of their own are called luminous bodies (C) Light is a form of energy (D) Objects that allow light pass through them are called opaque objects Statement I : Light can travel through vacuum Statement II : Light needs a medium to travel. (A) Both Statements are true, Statement - II is the correct explanation of Statement-I (B) Both Statements are true, Statement - II is not correct explanation of Statement - I. (C) Statement - I is true, Statement - II is false. (D) Statement - I is false, Statement - II is true. When the rays of light originating from a point, travel in various directions, then the collection of such rays is called (A) Parallel beam (B) Beam of light (C) Divergent beam (D) Convergent beam

Light 6.

7.

8.

47 When the rays of light travel parallel to each other, then the collection of such rays is called (A) Parallel beam (B) Beam of light (C) Divergent beam (D) Convergent beam When the rays of light coming from different directions, meet at a point then the collection of such rays is called (A) Parallel beam (B) Beam of light (C) Divergent beam (D) Convergent beam Choose the correct statements : (A) Any source of light which is bigger than point source of light is called extended source of light (B) A source of light which is of the size of pinhead is called point source of light. (C) An optical medium, which has different composition at different points is called heterogeneous medium. (D) An optical medium which has a uniform composition throughout is called homogeneous medium.

Conceptive Worksheet 1.

2.

3.

4.

5.

6.

Light travels in (A) Straight lines (B) Curved lines (C) Sometimes in straight lines sometimes in curved lines (D) Can’t say Sun is a (A) Luminous body (B) Non-luminous body (C) Transparent body (D) All of these Choose the correct statements: (A) Brick is a opaque body (B) Star is a luminous body (C) Sun is primary source of light (D) Light is an invisible energy A source of light which is of the size of the pin head is called (A) Point source (B) Extended source (C) Both (A) and (B) (D) Neither (A) nor (B) Light causes the (A) Sensation of smell (B) Sensation of sound (C) Sensation of sight (D) Sensation of touch A point source produces (A) Convergent beam (B) Divergent beam (C) Both (A) and (B) (D) Neither (A) and (B)

7.

Bodies which do not allow the light energy to pass through them are called (A) Transparent bodies (B) Translucent bodies (C) Opaque bodies (D) Optical medium

3. Rectilinear Propagation of Light Light travels in a straight line as long as it is travelling in the same medium. We can observe that light travels in a striate line when we observe the beam of a car headlight on a misty night or a beam of a torchlight entering a smoky room. We can also perform an experiment to demonstrate that light travels in a straight line. Experiment – 1 Aim: to demonstrate that light travels in a straight line Aids: three square cardboard sheets of equal size, plasticine of suitable stands, candle, knitting needle, iron nail. Method: 1. Take three cardboard squares of equal size. Locate the centre of each piece of cardboard by drawing the diagonals. 2. With the help of a nail, make a hole at the centre of each cardboard. 3.

Now fix the three cardboards on plasticine or on stands so that they remain upright.

4.

Arrange the three cardboards A, B and C, one behind the other such that their centres are in the same horizontal line. You may pass a knitting needle through the holes to confirm if they are in a straight line.

5.

Now place a burning candle in front of the board C and look through the pinhole in board A. The flame will be clearly visible. This shows that light travels in a straight line. Now, move board B slightly and again look through the pinhole in board A. You will not be able to see the flame. This shows that light does not travel in a zig–zag way.

Conclusion: light travels in a straight line. This property of light is called rectilinear propagation of light. www.betoppers.com

6th Class Physics

48

Rectilinear propagation of light

4. Pin Hole Camera 1. 2.

3.

Principle: It is based on the principle of rectilinear propagation of light. Construction: (a) It consists of a rectangular card board box, such that its one side is made of ground glass screen. (b) The side opposite to the ground glass has a hole of the size of pin head in its middle . (c) The box is blackened from inside so as to absorb any rays of light falling on its walls, directly or indirectly. Working: Consider an object AB in front of pin hole camera . The rays of light starting from various points of object travel in all direction. A ray of light starting from point A and travelling along AH, on passing through pin hole strike the screen at A1 . A

H

B

B’

A’ Similarly a ray of light, starting from point B along BH, on passing through pin hole strikes the screen at B1. Thus, the rays of light starting in between A and B will strike the screen between points A1 and B1 , thereby forming a small diminished image of object AB. 4. Nature of image formed by a Pin Hole Camera: The image formed by it is real and inverted image. The size of the image depends on the position of the object.

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5. Factors affecting the size of the image formed by a Pin Hole Camera: (a) The size of the image decreases as the object distance increases. (b) The size of image increases as image distance increases. 6. Magnification of Image: The ratio between the height of the image and height of the object is called magnification. It represents the number of times an image is magnified (or diminished) with respect to size of the object. Magnification 

Sizeof image  A'B' AB Sizeof object

7. Advantages of Pin Hole Camera 1. It does not require any lens and hence, the image is completely free from the defects of lenses. 2. It can take very sharp pictures of still objects. 3. It is cheap and easy to construct and operate. 8. Disadvantages of Pin Hole Camera 1. The time of exposure is too large and uncertain. Thus, the final image is either over-exposed or under-exposed. 2. It cannot take pictures of the moving objects. 3. It is cumbersome and not easy to operate. 4. If pin hole becomes wider, then the final image is blurred.

5. Reflection of Light When a beam of light is incident on a surface, a part of it is returned back into the same medium. The part of light which is returned back into the same medium is called the reflected light. The remaining part of light is absorbed if the surface on which the incident light strikes is opaque or it is partly transmitted and partly absorbed if the surface is transparent.

Light

49 Reflection: The return of light into the same medium after striking a surface is called reflection. Reflection of light is the process which enables us to see different objects around us. Luminous bodies are directly seen, but non luminous objects are seen only because they reflect the light incident on them which on entering into our eyes, make them visible.

The reflection which takes places from ground; walls; trees; suspended particles in air; and a variety of other objects, which are not very smooth, is irregular reflection. Irregular reflection helps in spreading light energy over a vast region and also decreases its intensity. Thus, it helps in the general illumination of places and helps us to see things around us.

6. General terms to the Reflection Note: Reflection is possible in case of plane mirror. A plane mirror is a plane glass plate which is silvered at its one surface. The other surface is then reflecting surface of the plane mirror. Types of Reflections: (a) Regular Reflection The phenomenon due to which a parallel beam of light travelling through a certain medium, on striking some smooth polished surface, bounces off from it, as parallel beam, in some other direction is called regular reflection. Regular reflection takes place from the objects like looking glass, still water, oil, highly polished metals, etc. Regular reflection is useful in the formation of images, e.g., we can see our face in a mirror only on account of regular reflection. However, it causes a very strong glare in our eyes.

(b) Irregular Reflection or Diffused Reflection: The phenomenon due to which a parallel beam of light, travelling through some medium, gets reflected in various possible directions, on striking some rough surface is called irregular reflection or diffused reflection.

(a) Mirror: A smooth polished surface from which regular reflection can take place is called mirror. MM| is the mirror as shown in figure. (b) Incident Ray: A ray of light which travels towards the mirror is called incident ray. AB is an incident ray in the figure. (c) Point of Incidence: The point on the mirror, where an incident ray strikes is called point of incidence. ‘B’ is the point of incidence in the figure. (d) Reflected Ray: A ray of light which bounces off the surface of a mirror, is called reflected ray. BC is reflected ray in the figure. (e) Normal: The perpendicular drawn at the point of incidence, to the surface of mirror is called normal. BN is the normal in the figure. (f) Angle of Incidence: The angle made by the incident ray with the normal is called angle of incidence.  ABN is the angle of incidence in the figure. (g) Angle of Reflection: The angle made by the reflected ray with the normal is called angle of reflection.  CBN is the angle of reflection in the figure. (h) Glance Angle of Incidence: The angle which the incident ray makes with the mirror is called glance angle of incidence.  MBA is the glance angle of incidence in the figure. (i) Glance Angle of Reflection: The angle which the reflected ray makes with the mirror is called glance angle of reflection.  M’BC is the glance angle of reflection in the figure.

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6th Class Physics

50 a)

Types of Images Virtual Image: When the rays of light, diverging from a point, after reflection or refraction, appear to diverge from another point, then the image so formed is called virtual image. I

Virtual Image

Plane mirror A

B

7. Laws of Reflection D

1.

The incident ray, the reflected ray and the normal lie in the same plane, at the point of incidence. 2. The angle of incidence is always equal to the angle of reflection. Formula for the angle of deviation due to Reflection In the figure angle of incidence = i; Angle of deviation = d

O Object

N A

B

i r M

O

M1

d

b) c

Consider the straight line AOC, i + r +d = 180° i.e., the sum of angle of incidence, angle of reflection and angle of deviation is 180°.  d = 180 – (i + r) = 180 – (i + i) (i = r)

 d  180 – 2i Therefore, for an angle of incidence i, the angle of deviation is equal to 180 – 2i =   2i Note: The deviation produced by n reflections from two plane mirrors inclined at an angle  is given by D = n(180 –  ) = 360 – 2  , if n = 2 where n is even.

8. Image When the rays of light, diverging from an object point, after reflection or refraction, either actually meet at some other point, or appear to meet at some other point, then that point is called image of that object.

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C

In figure the image ‘I’ of the object ‘O’ is virtual image. The ray of light diverging between OA and OB, after reflection, further diverges along AC and BD respectively. However, when these diverging rays of light reach the eye, then to the eye they appear to diverge out from point ‘I’. Thus I is virtual image of object ‘O’. Example: Image of our face in a plane mirror. Virtual images cannot be formed on a screen. Virtual images are always erect upright. w.r.t object The path of the rays forming a virtual image is shown by dotted lines. Real Image: When the rays of light, diverging from an object point, after reflection or refraction actually converge at some other point then that point is real image of that object. In figure the ray of light diverging from point A, after reflection from the concave mirror actually converge at the point A1. Thus, A1 is the real image of the point A. Concave mirror A

A

P

B B Real image

Example: Motion and still pictures projected on the screen in a cinema hall are real images. Real images are always inverted (upside down) w.r.t object . Real images and the path of the rays which form them are shown by continuous lines.

Light

51 Distinction between Real Image and Virtual Image: S.No

Virt ual image

1.

The r ays of light after reflection or r efraction appear to meet at some other point.

The r ays of light after reflection or refr action actually meet at some point.

2.

It cannot be caught on the scr een.

It can be caught on the screen.

3.

It is always erect.

It is always real.

4.

I mage of our f ace in plane mirr or is a virtual image.

Image for med on a cinema screen is a real image.

Characteristics of an image formed by a Plane Mirror 1. The image is formed behind the mirror and has the same size as the object 2. The image is inverted laterally. 3. The image is as far behind the mirror as the object is in front of it. 4. The image is virtual. It cannot be received on a screen. 5. The image is erected w.r.t object

Formative Worksheet 9.

10. 11.

12.

13.

14.

Real image

When a light ray is incident normally on the surface of a plane mirror, the reflected ray deviates through an angle of __________. What is the sum of angle of incidence , angle of reflection and angle of deviation equals to ? If the angle of deviation after reflection of a light ray is ‘d’, then find (a) angle of incidence (b) angle of reflection (c) angle of glancing Keeping the incident ray constant, if a plane mirror is rotated through an angle  , about an axis lying in its plane, then the reflected ray turns through an angle ___________. The angle between an incident ray and reflected ray for a given reflection is x. If the mirror is rotated through an angle x/2, keeping the incident ray constant, then find the angle between incident ray and reflected ray after rotation. Consider both clock wise and anticlock wise direction. Keeping the plane mirror fixed, if the incident ray is rotated through an angle  , then the angle through which the reflected ray rotates is _________.

15. A plane mirror lies face up, making an angle 15° with the horizontal. A ray of light shines down vertically on the mirror What is the angle of incidence? What will be the angle between the reflected ray and the horizontal be? 16. Statement I : The plane containing the incident ray and the normal is called plane of incidence. Statement II : The plane containing the incident ray and the normal is called plane of reflection. (A) Both Statements are true, Statement - II is the correct explanation of Statement- I. (B) Both Statements are true, Statement - II is not correct explanation of Statement - I. (C) Statement - I is true, Statement - II is false. (D) Statement - I is false, Statement - II is true. 17. Match the following: Column-I Column-II (A) Plane of reflection 1) The plane containing the reflected ray and normal

(B) Angle of deviation

2) The angle made by incident ray with the mirror

(C) Glancing angle

3) Angle through which a ray deviates from its normal path

(D) Normal

4) Perpendicular drawn to the surface at the point of incidence 5) The angle made by reflected ray with the mirror

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6th Class Physics

52 18. When the rays of light, diverging from a point, after reflection or refraction, appear to diverge from another point, then the image so formed is called (A) Virtual image (B) Real image (C) Both (A) and (B) (D) Neither (A) nor (B) 19. When the rays of light, diverging from a point, after reflection or refraction actually converge at some other point then that point is _____ image of the object (A) Virtual (B) Real (C) Both (A) and (B) (D) Neither (A) nor (B)

Conceptive Worksheet 8.

9.

10.

11.

12.

13.

14.

The image formed by a plane mirror is always: (A) Real (B) Erect (C) Virtual (D) Both (B) and (C) Reflection is possible in case of (A) Plane mirror (B) Transparent glass (C) Both (A) and (B) (D) Neither (A) nor (B) The part of light which is returned back into the same medium is called (A) Reflected light (B) Refracted light (C) Both (A) and (B) (D) Neither (A) nor (B) Motion and still pictures projected in a cinema hall are ______ images (A) Real (B) Virtual (C) Erect (D) All of these Choose the correct statements: (A) Regular reflection takes place on highly polished smooth surfaces (B) Irregular reflection takes place on rough surface (C) Irregular reflection is also called as diffused reflection. (D) On plane mirror regular reflection takes place. Image of our face in a plane mirror (A) Is a virtual image (B) Is a real image (C) Cannot be taken on the screen (D) Both (B) and (C) If a mirror is rotated by 10°, the reflected ray is rotated by (A) 10° (B) 20° (C) 40° (D) 30°

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15. Statement I : All the light rays actually converge at some point Statement II : All the light rays appears to converge at some point (A) Both Statements are true, Statement - II is the correct explanation of Statement- I. (C) Both Statements are true, Statement - II is not correct explanation of Statement - I. (B) Statement - I is true, Statement - II is false. (D) Statement - I is false, Statement - II is true. 16. Statement I : Real images are always inverted Statement II : Virtual images are always erect (A) Both Statements are true, Statement - II is the correct explanation of Statement- I. (B) Both Statements are true, Statement - II is not correct explanation of Statement - I. (C) Statement - I is true, Statement - II is false. (D) Statement - I is false, Statement - II is true. 17. When a mirror is rotated through an angle  the reflected ray from it, turns through an angle of

 (C) 2 (D) 0 2 18. The incident ray and the reflected ray from a mirror are mutually perpendicular to each other. The angle of incidence is (A) 90° (B) 45° (C) 22.5° (D) zero 19. A ray of light is incident on a plane mirror at an angle of 60° What is the angle of deviation? (A) 60° (B) 30° (C) 90° (D) 180° 20. An object situated at a distance of 10cm infront of a plane mirror. The distance of image from the mirror is (A) 10cm (B) 20cm (C) 5cm (D) some other value (A) 

(B)

9. Shadows We know that light rays travel in straight lines. Thus, if an opaque body is placed in the path of light rays, a dark patch is formed behind the opaque body. Dark patch formed behind on opaque body, when the opaque body is placed in the path of light is called shadow. There are two parts for a shadow. 1. Umbra: A region of total darkness, formed behind an opaque body, is called umbra. No rays of light reaches in this region.

Light

53 2.

Penumbra: A region of partial darkness, formed behind an opaque body, is called penumbra. Some rays of light always reach in this region and partially illuminate it.

Conditions for the formation of a Shadow: 1. There must be a source of light. 2. There must be an opaque object to obstruct the path of light. 3. There must be a screen to receive the shadow. Characteristics of a Shadow: When an opaque object is placed between a point light source and a screen, the shadow formed is 1. Uniformly dark 2. Sharp at the edges and 3. Of the same shape as the object. When an opaque object, larger than the light source, is placed between the light source and the screen, two patches are formed; umbra and penumbra. Formation of shadow by a Point Source of Light: When an opaque object is placed between a point light source and the screen, the shadow formed is (i) Uniformly dark (ii) Sharp at the edges and (iii) Of the same shape as the object.

Shadow formed by a point source

Characteristics of Shadow: (i) Only umbra is formed. (ii) The size of umbra increases, if the distance of screen from an opaque body increases and vice versa. (iii) The size of umbra increases, if the distance of the point source of light from an opaque body decreases and vice versa. Formation of Shadow by Extended Source of Light: An electric bulb or a burning candle, etc., are examples of luminous bodies acting as extended source of light. An extended source is made up of a large number of point sources. There can be the following two situations in case of an extended source of light.

(i)

When the extended source of light is smaller in size than the opaque body. (ii) When the extended source of light is bigger in size than the opaque body. (a) When extended Source is smaller than Opaque Body: When an opaque object, larger than the light source, is placed between the light source and the screen (position A), two patches are formed

(i)

The inner patch is completely dark as it does not get any light. This region is called umbra. (ii) The outer patch is not completely dark as it receives some light. This lighter patch of shadow is called penumbra. If the screen is moved away from the object (position B), both the umbra and penumbra increase in size Characteristics of Shadow: (i) Both umbra and penumbra are formed. However, size of the umbra is very large as compared to penumbra. (ii) If the screen is moved away from the opaque body, both umbra and penumbra increase and vice versa. (iii) If the source of light is moved towards opaque body, both umbra and penumbra increase and vice versa. (b) When extended source is bigger than Opaque Body: When an opaque object smaller than the light source is placed between the light source and the screen (position A), the umbra and the penumbra are formed.

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6th Class Physics

54

Light source larger than the object

The umbra is very small. If the screen is moved away from the object and from the light source (position B), the size of the umbra becomes smaller and smaller. Beyond a point, the umbra completely vanishes. Characteristics of Shadow: (i) Both umbra and penumbra are formed. However, size of the umbra is smaller than the penumbra. (ii) If the source of light is moved towards the opaque body, the penumbra increases, but the umbra decreases. (iii) If the screen is moved away from the opaque body, the penumbra increases and the umbra decreases, till a stage comes when no umbra is formed. Note: We cannot see the shadow or a kite of a bird flying high up in the air because the umbra is absent and the penumbra is too large and too faint to be visible.

Lunar Eclipse: The lunar eclipse occurs when the sun, earth and moon are in a straight line, with the earth in between the sun and the moon. The shadow of the earth is cast on the moon. If the moon is in the umbra cone of the earth, it will not be visible because the moon is non–luminous and since it does not receive any light from the sun, it does not reflect any light. This is called a total lunar eclipse.

If the moon is slightly out of line, it will not be completely in the umbra cone of the earth. It then receives some light from the sun which it reflects to the earth and makes itself partially visible. This is called a partial lunar eclipse. A lunar eclipse can occur only on a full moon day. Solar Eclipse: A solar eclipse occurs when the sun, earth and the moon are in a straight line, with the moon between the sun and the earth. The shadow of the moon is cast on the earth. The portion of the earth falling completely in the umbra region has total solar eclipse. The sun appears as a black circular disc with a ring of light. The portion of the earth falling in the penumbra region has partial solar eclipse. A solar eclipse can occur only on a new moon day.

Shadow of a flying bird is not visible

Eclipses: Eclipses are examples of the formation of shadows in the universe. The earth and the moon are opaque, non–luminous bodies and the sun is a luminous body. The earth and the moon cast their shadows leading to the phenomena of eclipses. At times, the sun, the earth and the moon come to lie in a straight line. The object in between casts a shadow and causes an eclipse. There are two kinds of eclipses, the lunar and solar eclipse.

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Formative Worksheet 20. Match the following Column-I Column-II a) Umbra i) Partial dark region b) Penumbra k) Total dark region (A) a-k, b-i (B) a-i, b-i (C) a-k, b-k (D) a-i, b-k

Light

55

21. When the sun, the earth and the moon come to lie in a straight line, it causes (A) Earth quakes (B) Eclipses (C) Eruption of volcanoes(D) Both (A) and (C) 22. A solar eclipse can occur only on a (A) New moon day (B) Full moon day (C) No moon day (D) None of these 23. Shadows are formed when light falls on (A) A transparent object (B) An opaque object (C) Both (A) and (B) (D) Neither (A) nor (B) 24. The completely dark portion of a shadow is called (A) Penumbra (B) Umbra (C) Both (A) and (B) (D) Neither (A) nor (B) 25. A solar eclipse is caused when the (A) Sun comes between the earth and the moon (B) Moon comes between the sun and the earth (C) The earth comes between the sun and the moon. (D) None of these 26. When the moon is in the penumbra of the shadow of the earth, what kind of eclipse occurs? (A) Solar eclipse (B) Total lunar eclipse (C) Partial lunar eclipse (D) No eclipse 27. A shadow which is partially illuminated is called (A) Umbra (B) Penumbra (C) Both (A) and (B) (D) Neither (A) nor (B)

(C) If sources of light is moved towards opaque body both umbra and penumbra increases (D) If source of light is moved towards opaque body penumbra increases umbra decreases 24. The formation of shadow by extended source of light when source is smaller than opaque body has (more than one answer possible) (A) Size of umbra is large compared to penumbra (B) Size of umbra is smaller than penumbra (C) If sources of light is moved towards opaque body both umbra and penumbra increases (D) If source of light is moved towards opaque body penumbra increases, umbra decreases 25. Statement-I : In most of the situations tube lights are preferred than bulbs Statement-II Tube lights form very faint shadows and may be called shadow less (A) Statement –I is true, statement –II is true and Statement –II is correct explanation of Statement I (B) Statement-I is true, Statement –II is true and Statement –II is incorrect explanation of Statement –I (C) Statement –I is true, Statement –II is false (D) Statement –I is false, Statement –II is true

Conceptive Worksheet 21. Shadows are dark patches formed behind an _____ body, when the ____ body is placed in the path of light. (A) Opaque, opaque

(B) Transparent, opaque

Summative Worksheet 1.

The image formed by a pin-hole camera is i and ii in size. The information in which alternative completes the given statement? (A)

(C) Opaque, transparent (D) Transparent, transparent 22. Light energy consist of tiny packets energy called (A) Electrons

(B) Photons

(C) Protons

(D) Neutrons

23. The formation of shadow by extended source of light when source is bigger than opaque body has (more than one answer possible) (A) Size of umbra is large compared to penumbra

(B)

(C)

(D)

i

ii

erect

diminished

i

ii

erect

magnified

i

ii

inverted

diminished

i

ii

inverted

magnified

(B) Size of umbra is smaller than penumbra www.betoppers.com

6th Class Physics

56 2.

3.

4.

Consider the following statements regarding shadows. I. Shadow is formed when a transparent object comes in the path of light II. Shadows can only be obtained on a screen III Whatever be the colour of an object, the shadow formed is always black or grey in colour Among the given statements, (A) Only statement I is correct (B) Only statement III is correct (C) Both statements I and II are correct (D) Both statements II and III are correct With reference to reflection, mirror changes the (A) Colour of light (B) Source of light (C) Intensity of light (D) Direction of light Alam is doing an experiment with a prism. He wants to project a beam of candle light on the prism. To do this, he has to make a hole on a cardboard sheet place it vertically between the candle and the prism (as shown in the given figure).

8.

Sohail tries to see through three different objects carbon paper, glass sheet, and tracing paper. He notes down his observations about visibility through these objects in tabular form. Which table correctly matches Sohail’s observations? (A)

5.

6.

7.

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Visibility

Carbon paper

Clear

Glass sheet

Not clear

Tracing paper Not visible at all

(B)

Object

Visibility

Carbon paper

Not clear

Glass sheet

Clear

Tracing paper Not visible at all

(C)

(D)

Where should Alam make the hole on the cardboard sheet? (A) I (B) II (C) III (D) IV Two coloured roses (red and white) are kept in front of a yellow light. What will be the colour of the shadows formed by red and white roses respectively? (A) Black and yellow (B) Red and white (C) Both yellow (D) Both black Which of the following set of objects can be used to form a shadow? (A) Magnet, iron, and screen (B) Magnet, wood, and screen (C) Bulb, glass, and screen (D) Bulb, book, and screen Objects that allow light to pass through them completely are known as (A) Translucent objects (B) Transparent objects (C) Luminous objects (D) Opaque objects

Object

9.

Object

Visibility

Carbon paper

Not visible at all

Glass sheet

Clear

Tracing paper

Not clear

Object

Visibility

Carbon paper

Not visible at all

Glass sheet

Not clear

Tracing paper

Clear

Objects are classified into three groups according to the amount of light passing through them. i objects allow light to pass through them completely.  ii objects allow light to pass through them partially. iii objects do not allow light to pass through them. The information in which alternative completes the given statements? (A)

i

ii

iii

Transparent

Translucent

Opaque

(B)

i

ii

Transparent

(C)

i

Opaque Translucent ii

Opaque

(D)

iii

iii

Translucent Transparent

i

ii

iii

Translucent

Transparent

Opaque

Light 10. A translucent object allows light to pass through it partially. Which of the following objects is a translucent object? (A) Plane mirror (B) Sand paper (C) Butter paper (D) Cardboard sheet 11. Amit tries to read a message written on paper through different materials. Amit will be able to read the message most clearly through a (A) Thin glass (B) Frosted glass (C) Tracing paper (D) Normal paper 12. Matthew’s teacher asks him to collect a sample each of transparent, translucent, and opaque materials. He collects a piece of glass as a sample of a transparent material and a piece of wood as a sample of an opaque material. As a sample of a translucent material, Matthew can use (A) An iron nail (B) A tracing paper (C) An air-filled glass tube (D) A water-filled glass tube 13. The shadows of red, blue, and black pens, formed on a white screen, appear (A) Red (B) Blue (C) Black (D) White 14. The shadow of a pen in the light of a candle suggests that (A) Light travels in a straight line (B) Light travels in a curved path (C) Pen is a transparent object (D) Pen is a translucent object 15. A clear shadow is obtained on a screen because it is formed by (A) An opaque object (B) A transparent object (C) The reflection of light (D) The refraction of light 16. One cannot see beyond the door of a closed room because it is (A) Transparent (B) Translucent (C) Refracting (D) Opaque 17. A transparent glass sheet can (A) Absorb light only (B) Refract light only (C) Absorb and reflect light (D) Reflect and refract light

57 18. An object that allows light to pass through it completely is called (A) Opaque (B) Luminous (C) Transparent (D) Translucent 19. Few objects were given to Mushtaq. He was asked to choose the translucent object amongst them. He made the perfect selection. Mushtaq made his selection by (A) Touching the objects (B) Putting them in water (C) Viewing through the objects (D) Placing a magnet near the objects 20. A conical object is placed in the path of a beam of light. Which of the following pictures may represent the shadow formed by the object? (A)

(B)

(C)

(D)

HOTS Worksheet 1.

2.

Jyoti places each of the four hollow tubes of different shapes between a torch and a screen (as shown in the given figure). The points on the screen at the end of the tubes are labelled as M, N, S, and T.

Which point on the screen will light up when the torch is switched on? (A) M (B) N (C) S (D) T On observing the given shadow, three students make three statements.

Student I: The object may be of a funnel Student II: The object may be of a bottle Student III: The object may be of a prism

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6th Class Physics

58

9.

The length of the shadow of a tree at noon is 3 m. What would be the length of the shadow of the tree in the evening? (A) 1m (B) 2m (C) 3m (D) 4m A ray of light is incident on a shiny surface as shown in the figure.

(D)

////////////////////

(C)

////////////////////

Which figure correctly represents the ray of light after it gets reflected by the surface? (A) (B) //////////////////// ////////////////////

The shadow of which of the following shapes cannot be obtained? (A) (B)

8.

////////////////////

3.

Among the given statements, the (A) Statement made by student I is correct (B) Statement made by student III is correct (C) Statements made by students I and II are correct (D) Statements made by students II and III are correct Jalal finds a conical object made up of cardboard sheets (as shown in the given figure). He brings it in sunlight and rotates it to obtain shadows of different shapes on ground.

10. The figure shows the shadow of a pole at noon. (C) 4.

(D)

Which glass jar will cast the darkest shadow? (A) Jar A (Fresh water) (B) Jar B (Coffee) (C) Jar C (Orange juice) (D) Jar D (Mustard oil)

5. Which of following objects will form the shadows shown above? (A) (B)

(C) 6.

(D)

David places an iron ball in front of a flash light. The ball will (A) Appear farther from the light (B) Appear closer to the light (C) Cast a shadow (D) Appear larger in size 7. The intensity of a shadow depends upon the intensity of the incident rays of light. During which time of day can the faintest shadows be observed? (A) Between 6:00 a.m. and 8:00 a.m. (B) Between 11:30 a.m. and 1:30 p.m. (C) Between 2:30 p.m. and 4:30 p.m. (D) Between 6:00 p.m. and 8:00 p.m. www.betoppers.com

Which figure correctly shows the shadow of the pole in the evening? (A) (B) (C) (D)

11. A clock hung on a wall of a hall has marks instead of numerals on its dial. On the opposite wall, there is a plane mirror and the image of the clock in the mirror indicates the time 7.40. hence, the time on the clock is (A) 7.40 (B) 4.20 (C) 5.40 (D) 10.7 12. An object is placed at a distance of 20 cm infront of a plane mirror. If the mirror moves towards the object by a distance of 20 cm, then find the displacement of the image. 13. An object is placed at a certain distance infront of a plane mirror. If both object and plane mirror moves towards each other through a distance of 15 cm, then find the distance through which the image moves. 14. If both object and mirror moves away from each other with a speed of 20 m/s, then find (a) The speed of the image (b) Speed of the image with respect to object (c) Speed of the image with respect to mirror.

Light

59

15. Two mirrors are inclined at a certain angle  . If a light ray is incident on the first mirror parallel to the second mirror and reflected from the second parallel to the first mirror, then find the value of  . 16. A man 180 cm high stands in front of a plane mirror. His eyes are at a height of 170 cm from the floor. Then the minimum length of plane mirror for him to see his full image is ___. 17. Two plane mirrors are inclined to each other at an angle of 70°. A ray is incident on one mirror at an angle  . The rays reflected from this mirror fall on the second mirror from where it is reflected parallel to the first mirror . What is the value of  ? 18. Two plane mirrors are inclined at an angle of 60° as shown in the figure. A ray of light parallel to Mirror1 strikes the Mirror 2. At what angle will the ray finally emerge? M2

600 M1

19. Two plane mirrors are placed parallel to each other. The distance between the mirrors is 10 cm. An object is placed between the mirrors at a distance of 4 cm from one of them, say M1. What is the distance between the first image at M1 and the second image formed at M2 ? 20. A plane mirror is moved away from a stationary object with a speed of 20 cm/s. What is the speed of the image?

IIT JEE Worksheet I.

Single Correct Answer Type

1.

Light is a form of (A) Energy (B) Force (C) Mass (D) None Artificial source of light is (A) Sun (B) Torch (C) Electric bulb (D) Both 2 and 3 Light shows (A) Rectilinear Propagation (B) Random Propagation (C) Curvilinear Propagation (D) None

2.

3.

4.

Parallel beam of light is (A) Light rays travel parallel to each other (B) Light rays starting from a point travel in various directions (C) Light rays coming from different directions meet at a point (D) All 5. Pinhole camera is based on (A) Rectilinear Propagation of light (B) Random Propagation of light (C) Curvilinear Propagation of light (D) None 6. A medium which partially allows the light to pass through it is called (A) Transparent (B) Opaque (C) Translucent (D) Luminous 7. Which of the following is a luminous body ? (A) Earth (B) Moon (C) Sun (D) None 8. When light from the sun enters into the atmosphere around the earth, its speed (A) Increases (B) Decreases (C) Remains same (D) None 9. The shadow below a tree has a bright spots in it, because (A) Leaves attract the light (B) The gap between the leaves acts as pin holes (C) Leaves reflect light (D) None 10. Shadow of the object becomes bigger (A) When the distance between object & screen is small (B) When the distance between object & screen increases (C) When the source of light is bigger than object (D) None 11. Shape of the shadow depends upon the (A) Size of the source of light (B) Distance between source of light and the object (C) Distance between object and the screen (D) Shape of the object

II. Multiple Correct Answer Type 12. Which of the following are the sources of light? (A) Sun (B) Star (C) Glow warm (D) Fireflies 13. Which of the following is a transparent medium ? (A) Glass (B) Pure Water (C) Air (D) Stone 14. To observe an object we need (A) Eyes (B) Light (C) Electricity (D) Sound www.betoppers.com

6th Class Physics

60 15. Which of following is correct regarding image formed by plane mirror ? (A) Image is Virtual (B) Laterally Inverted (C) Image is of same size as object (D) Image is real 16. Image through pin hole camera is (A) Real (B) Inverted (C) Small (D) Virtual

III. Paragraph Type Laws of Reflection (i) The incident ray, the reflected ray and the normal lie in the same plane, at the point of incidence. (ii) The angle of incidence is always equal to the angle of reflection.: Using the above information answer the following questions. 17. The incident ray and the reflected ray are at right angles. Then find the angle of incidence and the angle of reflection. (A) 45° each (B) 90° each (C) 30° each (D) 50° each 18. A ray of light is incident on a horizontal plane mirror at an angle of 45°. After reflection, from M1, some of the light is incident on another plane mirror. If the ray reflected by the second plane mirror travels horizontally, find the angle between the mirrors. (A) 50° (B) 22 ½° (C) 67 ½° (D) 90° 19. Two plane mirrors are inclined at an angle ‘  ’. It is found that a ray incident on one mirror at any angle is rendered parallel to itself after reflection from both the mirrors. Find the value of ‘  ’. (A) 90° (B) 45° (C) 35° (D) 75° 20. Two plane mirrors are inclined at 70°. A ray incident on one mirror at an angle  , after reflection, the reflected ray makes an angle of 30° with the second mirror. Find  . (A) 20°

(B) 10°

(C) 30°

(D) 40°

V. Matrix Matching 24. (A) Transparent Medium (p) Ground Glass (B) Translucent (q) Water (C) Opaque (r) Glow Warm (D) Luminous Body (s) Wood 25. (A) Speed (p) Vacuum (B) 500 seconds (q) 3 × 108 m/s (C) When light enters (r) Time taken by into denser medium light to reach the its speed earth (D) Speed of light is (s) Decreases maximum in (t) Increases 26. (A) Iron Block (p) Reflection of Light (B) Polished Surface (q) To take photographs of stationary objects (C) When moon comes (r) Opaque Medium between the sun and the earth (D) Pinhole camera (s) Solar Eclipse (t) Lunar Eclipse 27. (A) Image formed in (p) Lateral Inversion pinhole camera (B) Image in the plane (q) Inverted mirror (C) Shadows (r) Same colour of the Object (D) Images (s) Dark in colour (t) Erect 28. (A) Umbra (p) Region of partial darkness (B) Penumbra (q) Region of total darkness (C) Solar Eclipse (r) On full moon night (D) Lunar eclipse (s) On new moon day (t) Shadow 29. Match the following: (A) Ray of light

p)

(B) Parallel beam

q)

IV. Integer Type 21. If the angle between the mirror and the incident ray is 40°, the angle of reflection is ____°. 22. If the angle between the incident ray and the reflected ray is 100°, the angle of reflection is ____°

of light

(C) Divergent beam r)

23. A light ray is incident on a plane mirror making an

angle of 450 with respect to the surface of the mirror. the value of the angle between incident ray and reflected ray is ________° www.betoppers.com

of light (D) Convergent beam of light

s)

B y t h e en d o f t h i s ch a p t e r, y o u w i l l u n d er s t a n d  Electric Charge

 Symbols used in Electrical circuits

 Electric Current

 Connecting Electric Cells in Series

 Electric Cell

 Connecting Bulbs in Parallel

 Power Houses

 Conductors and insulators

Chapter - 5

Electricity

Learning Outcomes

 Electric Circuit

1. Introduction We use electricity for many purposes to make our tasks easier. For example, we us electricity to operate pumps that lift water from wells or from ground level to the roof top tank. We also use of electricity for lighting. Electricity makes it possible to light our homes, roads, offices, markets and factories even after sunset. This helps us to continue working at night. A power station provides us with electricity. However, the supply of electricity may fail or it may not be available at some places. In such situations, a torch is sometimes used for providing light. A torch has a bulb that lights up when it is switched on. Have you ever thought from where does the torch get electricity from?

2. Electric Charge In nature there are two types of charges. They are positive and negative charges. • Electric charges can exist independently either as positive or negative charges. • A positively charged body has more positive charges and negatively charged body has more negative charges. • A neutral body has equal amounts of positive and negative charges. • Positive charge is denoted by +q and negative charge is denoted by -q. • Unit: S.I unit of Charge is Coulomb. • Static electricity is study of electric charges at rest.

3. Electric Current Flow of charge in unit time is known as Electric Current. It is represented by ‘i’. • Electric Current ‘i’ = q/t; where ‘q’ is charge; ‘t’ is time.

• • • • • •

Unit: S.I unit of electric current is Ampere. Electric current has Electrical Energy. Electrical energy comes from electric cells. Electric current in our homes come form electrical generators or from power houses. In electric cells, current flows from positive terminal to negative through a metal wire. Electricity travels along a medium. It is generally a metal wire coated with plastic or rubber.

4. Electric Cell Electricity to the bulb in a torch is provided by the electric cell. Electric cells are also used in alarm clocks, wristwatches, transistor radios, cameras and many other devices. An electric cell has a small metal cap on one side and a metal disc on the other side .

It has a positive (+) sign and a negative (–) sign marked. The metal cap is the positive terminal of the electric cell. The metal disc is the negative terminal. All electric cells have two terminals; a positive terminal and a negative terminal. An electric cell produces electricity from the chemicals stored inside it. When the chemicals in the electric cell are used up, the electric cell stops producing electricity. The electric cell then has to be replaced with a new one. A torch bulb has an outer case of glass that is fixed on a metallic base

6th Class Physics

62 Filament

Terminals (a)

(b)

The thin wire that gives off light is called the filament of the bulb. The filament is fixed to two thicker wires, which also provide support to it. . One of these thick wires is connected to the metal case at the base of the bulb. The other thick wire is connected to the metal tip at the centre of the base. The base of the bulb and the metal tip of the base are the two terminals of the bulb. These two terminals are fixed in such a way that they do not touch each other. The electric bulbs used at home also have a similar design. Thus, both the electric cell and the bulb have two terminals each. Battery: A combination of two or more cells is called a battery. Button Cells: It is also a dry cells but are small in size and are used in calculators, wrist watches, etc. Storage Cells: A car battery or batteries being used in buses & trucks are combination of 6 or more cells inside. They can be recharged with the help of an electric charger & used again and again. For this purpose these batteries are also called accumulators.

Working of Torchlight: The source of energy for the torch are the electric cells inside the torch. • Small torches are with a single cell inside, while most torches have two or more cells. • When switched on , the metal strip inside the torch moves ahead and it touches the base of the reflector which holds the bulb. As soon as it makes contact with the reflector, the circuit is completed and the bulb lights up. • When switched off, the metal strip is pulled back. The contact of metal strip with the reflector is broken i.e., circuit is broken.

6. Electric Circuit An electric cell or dry cell is the source of energy for the bulb to glow and warm up. Let us now learn the way in which this electric energy is made available to the bulb in the torch. Making of a simple Electric Circuit Step 1: Take out the bulb from bulb from a torch. Examine the bulb carefully. The bulb is a small globe of thin glass enclosing a coiled filament supported on two thick wires. One of these thick wires is connected to the metal casing around the base of the bulb. The other wire is connected to the metal tip at the base. The metal casing and the metal tip at the base are the two terminals of the bulb.

5. Power Houses •

• •

For producing a large amount of electrical energy, big power houses are constructed. In these energy of flowing water or the energy of steam is converted into electrical energy. Energy generated in power houses is carried by electric cables to the cities and villages. When electric supply fails due to some reason, then electric generators provide electric current. In these diesel engine rotates the dynamo and converts the mechanical energy into electric energy.

Solar Cell: Solar cells are specially designed cells having solar panels. • Solar panels collect solar energy from sun and converts this solar energy into electrical energy. • This energy is used either directly or stored in an accumulator. www.betoppers.com

Inside a torch bulb

Step 2: Take two pieces of insulated wire. Insulated wires have metal wire inside with a plastic covering on the outside. Remove the plastic covering from both the ends of each piece of wire. Fix these wires on the bulb as shown in the figure with the help of Insulating adhesive tape. Or fix the bulb on a bulb holder. The two screws on the bulb holder are the two terminals which are connected to the two terminals on the bulb. The two pieces of wire be connected to the two terminals on the holder, as shown in the picture.

Electricity

63

Bulb connected with wires

Step 3: Connect the two free ends of the wires from the bulb or the bulb holder to an electric cell in such a way that one piece of wire is connected to the positive terminals of the cell and the other to the negative terminal of the cell. This may be done with the help of a rubber band or an adhesive tape. When you have finished with connections, the bulb lights up. With your finger trace the path of the electricity from the positive ( + ve) terminal on the cell to the negative (–ve) terminal of the cell. It is a round about path travelled by electricity. Closed and Open Circuit

(a)

(b)

The dry cell has two terminals. The central terminal of the dry cell is called positive terminal. The base of the dry cell (which is made of a metal) is called negative terminal. The above figure (a) shows the terminals of dry cell. The figure (b) shows the symbol for dry cell. The long line represents positive terminal of the cell and the small and thick line represents negative terminal of the cell. For this experiment you need a torch cell; a torch bulb marked 1.5 V, cellotape, a plastic coated 1 metre long copper wire and an old used blade. Cut the plastic coated copper wire into two halves A and B. Remove plastic coating from each end of the wire such that 1 cm of plastic is removed. Now

fix one bare end of each wire A and B to the terminals of 1.5 V bulb with the cellotape. Fix the other end of wire A to the base of cell with the help of cellotape. Now touch the bare end of wire B to the central terminal of cell as shown in figure. What do you observe? The bulb lights up. This shows that electric current is flowing in wire A and B through the bulb. The path along which electric current flows is called electric circuit. Now remove the wire B from the central terminal as shown in Fig. . What do you observe? The bulb does not glow. It is because electric current does not flow, if the path is broken or path is incomplete.

Closed Circuit or Complete Circuit

When the path which starts from one terminal of the cell, ends at the other terminal of the cell, without any break, then such a circuit is called complete circuit or closed circuit. When the circuit is closed, then any electric appliance in that circuit starts working. In the present case the bulb starts glowing. Open Circuit or Incomplete Circuit When the path of current, starting from one terminal of the cell to another terminal of the cell is broken or incomplete, then such a circuit is called open circuit or incomplete circuit. For example, when we remove wire B from central terminal of cell, then the circuit is open circuit or incomplete circuit. Switches are used in the household wiring^ to open or close the electric circuit. When we switch on a particular electric appliance, we close the electric circuit. Conversely, when we switch off an electric appliance, we open the electric circuit.

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6th Class Physics

64

7. Symbols used in Electrical Circuits

A switch, a simple device to ‘close’ or ‘open’ a circuit: An electric circuit passes through a switch. Switch is a simple device which helps us to close or open the circuit. It helps in saving electricity when not in use. You are always advised to switch ‘off the lights or other gadgets in your home to save electricity. Ammeter is used to measure the current and voltmeter is used to measure the potential difference. More details of ammeter and shall be learnt is voltmeter higher classes.

8. Connecting Electric Cells in Series

of the second are connected to the bulb. The bulb now glows brighter. In the battery torch or battery light two or three dry cells are put into a metal container in series. The positive of one cell is connected to the negative pole of another cell in the series connection, When the, switch is turned on, the circuit is closed and the bulb glows and gives light. Connecting Electric Cells in Parallel Take three dry cells and connect them as shown in fig.. That is all the positive poles of the three cells are connected together, and all the three negative poles are connected together.

Take a dry cell and a torch bulb. Connect the bulb to the cell using copper wires as shown in Fig. . Observe the intensity- of light. The bulb does not glow brightly.

Now take one more dry-cell and connect two cells as shown in figure. In this method the positive of the first cell is connected to the negative of the second. The negative of the first and the positive www.betoppers.com

These three positives and three negatives are connected to the bulb- You will observe that there is no change in the brightness of the bulb! When cells are connected in parallel, their total electromotive force is the same as that if any one of them.

Electricity

65

When cells are connected in series, their electromotive force is equal to the sum of the EMF of all the cells used. Connect three torch bulbs in series as shown in figure. Connect this to a dry cell and observe that brightness of each of the three bulbs. Now connect one more dry cell in series with he first cell. Observe the brightness of each of the bulb. Then connect one more dry cell in series with the first two cells. Again observe the bulbs.

Both the bulbs will stop glowing. Now remove the bulb B and instead fix a fused bulb C as in the above figure. What is your observation? Bulb A does not glow.

Disconnect one of the three bulbs in the circuit. The circuit becomes open and all the three bulbs stop glowing. In series connection of bulbs,’ if one bulb gets fused, all the other bulbs in the series will stop working. Three bulbs connected in Series

9. Connecting Bulbs in Parallel Connect three bulbs in parallel. That is, one end of each of the three bulbs are connected one wire, the other ends of the three bulbs are con nected to another wire! These two wires are con nected to a dry cell. All the three bulbs glow dimly. Now disconnect one of the bulbs. The other bulbs continue to glow as before.

1.

2. 3.

To study the properties of (i) Series circuit, (ii) Parallel circuit Materials required : a battery of four cells two bulbs of 1 watt each one fused bulb a switch few lengths of connecting wires cellotape.

Following are the conclusions from the above investigation. In series circuit all the appliances work simultaneously when switch is closed. Conversely, all appliances stop working when switch is open. In series circuit, if any, of the appliances goes out of order, the other appliances stop working. As the bulbs were not glowing very brightly, it can be concluded that in series the appliances do not work to their full capacity. Now connect the bulbs A and B in parallel, such that they have common positive and common negative terminals as illustrated by Fig. , through a switch and a battery. Close the switch. What do you observe? Both the bulbs A and B glow very brightly. Now remove the bulb B and instead fix a fused bulb C Fig. . What is your observation?

Method: Connect the bulbs A and B in series by connecting them to connecting wires with the help of cellotape as shown above. Connect the free ends of connecting wires to a battery through a switch. Close the switch. What do you observe? Both the bulbs will glow. However, they will not glow very brightly. Open the switch. What do you observe? www.betoppers.com

6th Class Physics

66

1. 2.

3.

The bulb A continues glowing brightly, whereas bulb C does not glow. Following conclusions can be drawn from above investigation. In parallel circuit all the appliances work independently In parallel circuit if one appliance goes out of order, the other continues working. It means that each appliance in parallel circuit can be operated independently by a switch. As the bulbs glow brightly, it means each appliance gets enough electric energy, and hence, works to its full capacity.

6.

10. Conductors and Insulators The materials which allow the electric current to pass through them are the conductors of electricity and the materials through which electric current does not pass are the non-conductors or the bad conductors of electricity. Metals are the conductors of electricity. Non metals like glass, plastic, wood, paper, cloth and rubber are the non-conductors of electricity. Non-conductors of electricity are also called insulators. All leads (wires) being used in an electric circuit are metallic wires coated with plastic or rubber. Coating of a conductor with a non-conductor is called insulation. If we happen to touch a metallic end of a lead through which current is passing, it gives an electric ‘SHOCK’. The shock may be fatal too or otherwise it shakes the body and harms the person who has suffered the electric shock. Insulation saves a person from electric shock.

Formative Worksheet 1.

2. 3. 4.

5.

If a current of 10 mA passed through your cell phone battery charger wire for 10 minute , what quantity of electric charge is transferred through the wire to the battery? How much current does your laptop consume if 100 C of charge is transferred through the charger wire in 4 second ? How much time is required for 10 Coulombs of charge to flow past a point if the current is 2 amperes? Which of the following materials is a good conductor of electricity? (A) Plastic (B) Cork (C) Soil (D) Iron The handle of every electrical repairing tool is covered by a certain material to prevent the user from getting an electrical shock.

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7.

8.

9.

Which of the following materials cannot be used to cover the handle of an electrical repairing tool? (A) Tin (B) Glass (C) Wood (D) Rubber Mason constructs the circuit shown in the figure. He leaves a gap in the circuit to test the conductivity of various materials.

On inserting which of the following materials in the gap will the bulb not light up? (A) Wood (B) Iron (C) Aluminium (D) Silver Which of the following objects is an insulator? (A) Iron rod (B) Plastic cup (C) Nickel coin (D) Steel spoon Martin is constructing an electrical circuit. He notices that all electrical metal wires are covered with plastic. Electrical metal wires are covered with plastic because plastics are good (A) Electrical conductors (B) Electrical insulators (C) Heat generators (D) Heat absorbers Tommy sets up an electrical circuit as shown in the figure. He connects points P and Q with different materials.

The bulb will light up when points P and Q are connected by a plate made of (A) Iron (B) Glass (C) Wood (D) Plastic 10. Brad sets up an electrical circuit as shown in the given figure. He connects points P and Q of the circuit with four different rods made of four different materials - glass, wood, copper, and asbestos.

The bulb in the circuit will not light up when points P and Q are connected with (A) Glass rod (B) Wood rod (C) Copper rod (D) Asbestos rod

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11. Ronald wants to make electrical wires with a wire (A) drawing machine. He considers using steel, copper, aluminum, and plastic as raw material. The material that Ronald cannot use to make electrical wires is (A) Steel (B) Copper (C) Plastic (D) Aluminum (B) 12. Margaret notices that there are ceramic pulley-like structures attached to the overhead electrical lines near her house. Electrical wires pass over the pulleys as shown in the given figure. These pulleys are used as electrical (A) Insulators (B) Generators (C) Conductors (D) Transformers (C) 13. Which of the following materials cannot be used as an electrical insulator? (A) Wood (B) Rubber (C) Plastic (D) Graphite 14. John is repairing the electrical line of his house. As a precautionary measure, he stands on a wooden plank. John uses the wooden plank because wood (D) is (A) An electrical conductor (B) An electrical insulator (C) A heat conductor (D) A heat absorber 15. The given figure shows a simple circuit consisting 17. The given figure shows a simple circuit involving a of a bulb and a switch. battery, a switch, and a bulb.

On closing the switch, the bulb will (A) Glow (B) Not glow (C) Glow after some time (D) Glow only for a short time 16. The given figure shows four wires, a switch, a bulb, and a battery.

The bulb will glow when the given components are connected as

If the terminals of the battery are reversed, then the bulb will (A) Glow (B) Not glow (C) Glow for a short time (D) Glow after some time 18. A simple electrical circuit containing two bulbs and a battery is shown in the given figure.

If bulb 1 fuses on closing the switch, then bulb 2 will (A) Keep glowing (B) Stop glowing (C) Glow brightly (D) Glow dimly www.betoppers.com

6th Class Physics

68 19. The symbol for a fuse is (A) (C)

27. Greater potential difference (or emf ) is obtained in the circuit when cells are connected in (A) Series (B) Parallel (C) Both (A) and (B) (D) Neither (A) nor (B)

(B) A

(D)

20. The symbol for a ammeter is (A) (C)

A

(B)

V

(D)

()

Conceptive Worksheet 1.

21. In a parallel circuit of bulbs (A) Same current exists in all the bulbs (B) Same voltage exists in all the bulbs (C) Failure of any bulb leads to a break down in the circuit (D) All of above 22. Column-I Column-II a) Cell b) Resistance c) Closed switch d) Voltmeter 23.

24.

25.

26.

1) V 2) 3) 4) ( ) 5) () When negative terminal of a cell is connected to the positive terminal of the next cell are said to be in (A) Series (B) Parallel (C) Both (A) and (B) (D) Neither (A) nor (B) When electric cells are connected in series the electromotive force (A) Increase (B) Decreases (C) Remain same (D) become zero Choose the correct option (A) The path along which electric current flows is called electric circuit (B) Coating of a conductor with a non-conductor is called insulator (C) The materials which allow the electric current to pass through them are called conductors (D) The materials which allow the electric current to pass through them are called nonconductors If a voltage V is applied across the bulbs in series, then (A) The voltage applied is divided among the bulbs (B) The same current exists in all the bulbs (C) The same voltage exists in all the bulbs (D) The current is divided among the bulbs

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2.

3.

4.

5.

The given figure shows a simple circuit containing four bulbs and five switches along with a battery.

What is the minimum number of switches that must be closed to light at least one bulb? (A) 1 (B) 2 (C) 3 (D) 4 The handle of every electrical repairing tool is covered by a certain material to prevent the user from getting an electrical shock. Which of the following materials cannot be used to cover the handle of an electrical repairing tool? (A) Tin (B) Glass (C) Wood (D) Rubber The given figure shows a simple circuit that consists of a bulb, a battery, and two switches.

In the given circuit, when switch I is closed, the bulb will (A) Glow (B) Flicker (C) Not glow (D) Flicker after some time Which of the following materials is a good conductor of electricity? (A) Plastic (B) Cork (C) Soil (D) Iron Robert constructs an electrical circuit as shown in the given figure. Four different points are labeled as P, Q,R, and S on the wooden rod.

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6.

69

In the given circuit, the bulb will glow when the positive terminal of the battery is connected to the 9. point (A) P (B) Q (C) R (D) S In which of the following circuits can the electrical bulb be operated using the switch in the circuit? (A)

(C)

7.

Alex should add the switch at point (A) I (B) II (C) III (D) IV The given figure shows a simple electrical circuit that consists of two bulbs, and a battery. One switch has to be added to the circuit in order to operate only bulb M.

(B)

(D)

This switch must be placed at point (A) I (B) II (C) III (D) IV 10. The given figure shows two bulbs, a switch, a battery, and a fan. Using all the components, David makes a simple electrical circuit putting a bulb on either sides of the fan.

The circuit shown in the given figure consists of a fan, a switch, and a battery. Andrew wants to connect a bulb in parallel to the fan. Which of the following circuit diagrams represents the one made by David?

Andrew should connect the bulb in the electrical circuit as shown in figure (A)

(C)

8.

(A)

(B)

(C)

(D)

(B)

(D)

Alex constructs the electrical circuit shown in the given figure in his school laboratory. His teacher asks him to add a switch to the circuit such that only bulbs N and P are operated by it.

11. The given figure shows two bulbs, a switch, and a battery. Martha makes a simple circuit using all the given components. The circuit is such that a bulb is placed on either sides of the switch.

Which of the following circuit diagrams represents the one made by Martha? (A) (B)

(C)

(D)

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6th Class Physics

70 12. An electric circuit made by a student is incomplete because one of the wires is too short to connect with the other wire as shown in the given figure. In order to glow the bulb, he has to connect the open ends by inserting an object between them.

16. The path along which electric current flow is called (A) Electric circuit

(B) electric shock

(C) Both (A) and (B)

(D) neither (A) nor (B)

17. Which of the following are the non-conductors of electricity (A) Wood Which of the following objects should the student insert between the open ends? (A) Nail (B) Bottle (C) Glass sheet (D) Rubber band 13. Which of the following objects can conduct electricity? (A)

(B)

(C)

(D)

18.

19.

14. The given figure represents four circuit arrangements, I., II, III,  and IV.  Each  circuit consists of an electric cell and a torch bulb.

20.

21. 22.

(B) Paper

(C) Cloth (D) Rubber Statement I : Switch is used to close are open electric circuit Statement II : When switch is closed , then circuit is closed and when it is opened, then circuit is open circuit (A) Both Statements are true, Statement - II is the correct explanation of Statement- I. (B) Both Statements are true, Statement - II is not correct explanation of Statement - I. (C) Statement - I is true, Statement - II is false. (D) Statement - I is false, Statement - II is true. What is the total emf , when three cells of emf’s are 2V,2.5V, 4V are connected in series (A) 4V (B) 2.5V (C) 2V (D) 8.5V What is the total emf, when three cells of emfs are 2V, 2V, 2V are connected in parallel (A) 4V (B) 1V (C) 2V (D) 5V The total emf of three cells of emf’s 1v,1v,1v are connected in series is ____v Which of the following is used as source of electrical energy (A) Electric cell (B) Dry cell (C) Ammeter (D) Voltameter

Summative Worksheet The bulb  may  glow  in  the  circuit  arrangements labelled as (A) I and II (B) II and III (C) III and IV (D) IV and I 15. An electric cell has i terminal(s). The metal cap of an electric cell represents its ii terminal. The information in which alternative completes the given statement? (A)

(C)

i

ii

two

negative

i

ii

one

negative

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(B)

(D)

i

ii

two

positive

i

ii

one

positive

1.

Electric current flows from ___ terminal to ___ terminal outside the cell through the circuit.

2. 3.

represents. In which case, bulb glows in the circuit. (A)

(B)

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71

(C)

HOTS Worksheet 1.

(D)

It is impossible to construct a torch in the absence of (A) Plastic casing (B) Electric cells (C) Reflector (D) Switch

2.

3. 4. 5. 6.

7.

(A) A (B) B (C) C (D) D Is pure water a conductor of electricity ? Electric current flows in ___ direction only. A cell has two terminals, one terminal is on the metal base, second terminal is on ___. Bulb in this circuit doesn’t glow; why?

A device that is used to break an electric circuit is called ? 8. An electric cell has ___ terminals. 9. Unit of electric current is ___. 10. Match the following (i) Battery (a) Rechargeable Batteries (ii) Accumulator (b) A combination of two or more cells (iii) Closed Circuit (c) An unbroken path of electricity (d) The path along which electricity travels (A) i - b, ii - c, iii - d (B) i - a, ii - b, iii - c (C) i - b, ii - a, iii - c (D) i - c, ii - d, iii - a 11. (i) Button Cells (a) Torch light, Clocks (ii) Dry Cells (b) Wrist watches, Calculators (iii) Accumulators (c) In Cars, Trucks (d) Space Satellites (A) i - b, ii - a, iii - c (B) i - b, ii - a, iii - d (C) i - c, ii - d, iii - b (D) i - a, ii - b, iii - a

3.

4.

Among the labelled parts, current does not flow through the (A) Battery (B) Switch (C) Filament (D) Reflector The given figure shows a circuit with a cell connected to a bulb and a switch.

When the switch is closed, the bulb lights up because the (A) Switch produces electricity (B) Switch produces electricity (C) Connecting wires produce electricity (D) Circuit completes on closing the switch Atul has constructed four electric circuits, each consisting of a bell, a bulb, switch and a cell. The bells of the circuits are labelled as 1, 2, 3, and 4, as shown in the given figure.

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6th Class Physics

72

5.

6.

Which bell will produce a sound when the switch is closed? (A) Bell 1 (B) Bell 2 (C) Bell 3 (D) Bell 4 Suraj has constructed a simple electric circuit. It consists of a bulb, a switch, and a cell, as shown in the given figure. However, the lengths of the wires are not sufficient. Hence, this circuit has two free ends. He has four objects namely a wooden gilli, a match stick, a pen cap, and a nail.

To glow the bulb, Suraj should connect the free ends with the (A) Nail (B) Matchstick (C) Pen cap (D) Wooden gilli Raju has constructed four different circuits with four bulbs, four cells, and four different objects, as shown in the given figure.

8.

9.

The given figure shows two circuits, each consisting of a bulb and a cell. M and N are the terminals of cell I and S and T are the terminals of cell II. The direction of current in the respective circuits is indicated by arrowheads.

Terminals M and T of the cells are (A) Both positive (B) Both negative (C) Positive and negative respectively (D) Negative and positive respectively A circuit is constructed using two torch bulbs and a cell, as shown in the given figure at the left. The figure at the right shows four arrows whose tips show their respective directions. These arrows have to be placed on each wire segments RS, RV, ST, and TV respectively, according to the directions of current.

The given arrows that can be placed on wire segments RV, VT, ST, and RS are respectively

7.

Which bulb will glow in the given circuits? (A) , , , and  (B) , , , and  (A) Bulb 1 (B) Bulb 2 (C) Bulb 3 (D) Bulb 4 (C) , , , and  (D) , , , and  Raju bought five similar bulbs and connected them 10. Various parts on the outer surface of an electric with two cells to construct an electric circuit. The cell are labelled as I, II, III, and IVrespectively in given figure shows the circuit constructed by Raju. figure (a). In figure (b), an incomplete circuit is shown. M and N are the free ends of this circuit.

In the given circuit, the bulbs that would not glow are (A) Bulb 1 and Bulb 2 (B) Bulb 2 and Bulb 3 (C) Bulb 3 and Bulb 4 (D) Bulb 4 and Bulb 5

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To make the bulb glow, free ends M and N of the circuit should be respectively connected to (A) I and II (B) II and III (C) III and IV (D) IV and I

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73

11. Which of the following parts of a torch is not paired 14. The picture of a household torch is shown is the with its function? given figure. (A) Part of a torch

Bulb (B) Part of a torch

Switch (C) Part of a torch

Reflector (D) Part of a torch

Cell

Funct ion Emits light Funct ion Breaks the circuit Function Completes the circuit Function

The electricity required to operate a simple torch is provided by the (A) Bulb (B) Electric cell (C) Switch (D) Curved mirror 15. Different arrangements of an electric bulb with an electric cell are shown in the given figure. The arrangements are labelled as M, N, S, and T respectively.

Provides energy

12. Raj performs an experiment to know the conducting nature of some of the objects using a circuit, as shown in the given figure. He inserts some objects one by one between M and N and observes whether the bulb glows or not. The objects that he inserted are eraser, key, plastic scale, glass bangle, bottle cap, nail, thermocol sheet, and wallet.

Raj will be able to glow the bulb if he inserts (A) Key and nail respectively (B) Key, nail, and wallet respectively (C) Bottle cap and thermocol sheet respectively (D) Eraser, scale, bangle, and bottle cap respectively I. 13. The schematic diagram of an open circuit is shown 1. in the given figure.

2. Which of the following objects is inserted tightly in the gap to make the bulb glow? 3. (A) Key (B) Cork (C) Plastic bottle cap (D) Thermocol sheet

The bulb will glow in (A) Arrangement N only (B) Arrangement T only (C) Both arrangements M and N (D) Both arrangements S and T

IIT JEE Worksheet Single Correct Answer Type The metallic wires used for connections in an electric circuit is called. (A) Leads (B) Cells (C) Batteries (D) Insulators Most handy source of electricity which is used in torch lights are. (A) Dry Cells (B) Button Cells (C) Batteries (D) None In wrist watches ___ are used. (A) Dry Cell (B) Button Cell (C) Battery (D) None

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6th Class Physics

74 4.

Metals are ___ of electricity. (A) Conductors (B) Non Conductors (C) Both (D) None

5.

represents.

(A) Electric Switch (B) Battery (C) Cell (D) Fuse 6. Electricity name was given by ___. (A) Thales (B) Gilbert (C) Newton (D) Coulomb 7. Combination of two or more cells is called ___. (A) Battery (B) Accumulators (C) Button Cells (D) None 8. ___ is a non-metal but is a Conductors of electricity (A) Graphite (B) Glass (C) Mercury (D) Water 9. Electric current flows from ___ terminal to ___ terminal outside the cell through a circuit. (A) Positive, Negative (B) Negative, Positive (C) Both (D) Cannot say 10. An electric cell converts ___ energy into electrical energy. (A) Chemical (B) Mechanical (C) Wind (D) Light 11. Which of the following energy conversions take place in a torch. (A) Electrical Chemical Light (B) Chemical Electrical Light (C) Electrical Light Chemical (D) Light Chemical Electrical 12. Which of the following is an insulator? (A) Pure Water (B) Impure Water (C) Human Body (D) Earth 13. Car battery and mobile phone battery are rechargeable. Hence these are called ___. (A) Dry Cells (B) Accumulators (C) Button Cells (D) None 14. There are two types of charges, they are ___ and ___. (A) Positive & Neutral (B) Negative & Neutral (C) Positive & Negative (D) None 15. S.I unit of Charge is (A) Ampere (B) Volt (C) Newton (D) Coulomb www.betoppers.com

16. The shorter, thicker vertical line in the symbol of Cell represents. (A) The positive terminal (B) The negative terminal (C) The direction of current (D) All of these 17. Over head electric cables passing through poles are NOT insulated because. (A) Insulation will cause energy loss (B) Air is a bad conductor (C) The wires will get heated (D) It is costly 18. Photovoltaic cells produce electricity by using. (A) Wind Energy (B) Solar Energy (C) Geothermal Energy (D) Mechanical Energy of Water 19. What happens to a circuit when the switch is off. (A) The circuit is complete (B) There is a gap in the circuit (C) Electricity flows continuously (D) Electricity flows discontinuously

II. Multiple Correct Answer Type 20. The symbol for switch (A)

(B)

(C) (D) () A 21. Which of the following are conductors? (A) Silver (B) Copper (C) Aluminium (D) glass 22. Which of the following are insulators? (A) Glass (B) Plastic (C) Wood (D) Silver

III. Paragraph Type The rate of flow of charge in a circuit is called electric current. In other words, it is the amount of charge flowing per second. It is denoted by the letter I. If Q is the charge which is flowing through a conductor in time t, then current is given by i 

Q t

Unit of Current: The S.I unit of current is ampere and it is denoted by the letter ‘A’. The S.I unit of Q is coulomb and that of t is second.

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75

Thus, the S.I unit of electric current is

IV. Integer Type

1 coulomb  1A 1 second

26. The current passing through a conductor is 5 ampere .Then the charge that passes through that conductor in 5 minute is _______Coulomb 27. If 60 coulomb of charge passes through a cross section of a conductor in 4 sec, the average current is_________A 28. A light ray is incident on a plane mirror making an angle of 450 with respect to the surface of the mirror. The value of the angle between incident ray and reflected ray is ________°

Using the above answer the following questions. 23. If there is a current of 10 amperes in a circuit for 10 minutes, what quantity of electric charge flows in through the circuit? 24. How much current must there be in a circuit if 100 coulombs flow past a point in the circuit in 4 seconds? 25. How much time is required for 10 coulombs of charge to flow past a point if the rate of flow (current) is 2 amperes?

V. Matrix Matching 29. (A) Conductor (B) Insulator (C) Outside the cell through circuit

(p) Wood (q) Graphite (r) Electric current flows from positive to negative (s) Electric current flows from negative to positive

30. (A) Solar panels (B) Cells (C) Windmills (D) Dams

(p) Wind energy into electrical energy (q) Heat energy into electrical energy (r) Chemical energy into electrical energy (s) Solar energy into electrical energy (t) Potential energy of water into electrical energy

31. (A) A path along which electric current flows (p) Switch (B) A device which converts chemical energy into (q) Electric circuit electric energy (C) A device which makes or breaks the circuit (r) Cell (s) Electric current 32. (A) Cell

(p)

(B) Bulb

(q)

(C) Switch

(r) (s)

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6th Class Physics

B y t h e e n d o f t h i s c h a p t e r, y o u w i l l u n d er s t a n d  Natural and Artificial Magnets

Chapter - 6

Magnetism

Learning Outcomes  Properties of a magnet  General Definitions of Bar Magnet

1. Introduction People have known about magnets since ancient times. The first known magnets were hard black stones called “loadstones “. Throughout the middle Ages many people believed that loadstones had medical powers. During this period, it was discovered that a loadstone would point to the north. Magnetism is the term used to describe the phenomenon by which forces attract some bodies to each other and to the forces which act between electric currents. Magnetism is an important force in nature that makes possible everyday happenings like talking on the telephone, watching television, listening to taped music and storing data (sound and images) on computer discs. Compasses made with magnets help navigators guide ships safely. Without magnetism, it would not be possible to produce large amounts of electricity and neither could we use electricity to do all the jobs it does. William Gilbert a physician was the first to use the terms magnetic pole and electrical force. It was he who suggested that the Earth’s magnetism could be explained if the Earth was likened to a huge bar magnet. Real progress in understanding magnetism came after the relationship between electricity and magnetism was established by Hans Christian Orested in 1820. What is Magnetism ? Just like when the Greeks of the old times discovered the first naturally occurring magnetic stones, or natural magnets, you have been observing a property of matter called magnetism. Magnetism is the force of attraction or repulsion in and around a material.

Magnetism is present is all materials but at such low levels that it is not easily detected. Certain materials such as magnetite, iron, steel, nickel, cobalt and alloys of rare earth elements, exhibit magnetism at levels that are easily detectable.

What is a Magnet ? A magnet is any piece of material that has the property of attracting iron (or steel). Magnetite, also known as lodestone, is a naturally occurring rock that is a magnet. This natural magnet was first discovered in a region known as magnesia and was named after the area in which it was discovered. Magnetism may be naturally present in a material or the material may be artificially magnetized by various methods. Magnets may be permanent or temporary. After being magnetized, a permanent magnet will retain the properties of magnetism indefinitely. A temporary magnet is a magnet made of soft iron, that is usually easy to magnetize; however, temporary magnets lose most of their magnetic properties when the magnetizing cause is discontinued. Permanent magnets are usually more difficult to magnetize, but they remain magnetized. Materials which can be magnetized are called ferromagnetic materials. We will talk more about making a magnet later on.

6th Class Physics

78 Magnetic and Non Magnetic Materials SUBSTANCES

Magnetic Substances Substances which are influenced or affected by a magnet is called a magnetic substances. Ex: Iron, steel, nickel, Cobalt etc.

Non-Magnetic Substances Substances which are neither attracted nor repelled by a magnet are called non-magnetic substances. These cannot be magnetised. Ex: Paper, wood, glass etc.

Types of Magnetic Substances We are familiar with substances which are attracted by magnets. But it is interesting to note that there are certain substances which are repelled by a magnet. So, based on the property of attraction or repulsion, magnetic substances can be broadly divided into three classes, namely Ferromagnetic. Paramagnetic and Diamagnetic substances.

Ferro Magnetic The substances which are strongly attracted by a magnet and can be easily magnetised to form strong magnets are called Ferro magnetic substances.

Para Magnetic The substance which are very feebly attracted by a magnet are called Para magnetic substances.

Dia Magnetic The substances which are feebly repelled by a magnet are called Dia magnetic substances.

Ex: Iron, steel, nickel, cobalt Ex: Paltinum, Zinc, manganese, Ex: Copper, gold, bismuth, and their alloys etc. wood, aluminium, plastic etc. antimony, water etc.

2. Natural and Artificial Magnets Magnets are four types, viz ..Natural , Artificial , Temporary and Permanent magnets. Natural Magnets A substance which possesses the property of attracting small pieces of irons, steel, cobalt, nickel is called a magnet and this property is called attractive property. The magnets found in nature are called natural magnet. They are found in quite irregular and odd shapes. Example of a natural magnet is a “lodestone”.

property was used by sailors to navigate their ships. Hence a natural magnet is also called ‘lodestone or leading stone’ (from old English ‘lad for way). The modern name Magnetite derives its origin from the locality in which the mineral was first found in large quantities, namely, the town of Magnesia, in Asia Minor. Magnetite is found occurring naturally in many parts of the world. It is black oxide of iron with the chemical formula Fe3O4 and is natural magnet. It was magnetite that allowed people to get acquainted with magnetic properties of bodies. Natural magnets are not magnetically strong enough for practical purposes, Therefore, artificial magnets are required. Artificial Magnets

Load stone

When a piece of lodestone is suspended by a fine thread it comes to rest in north-south direction. This property is called directive property. This www.betoppers.com

Natural magnets like the lodestone do not have very strong attractive or directive properties, but when a piece of steel is stroked (in one direction only) with a lodestone, these properties are developed stronger in it.

Magnetism

79

A piece of steel or iron to which the properties of a lodestone have been imparted is called an artificial magnet.

Types of Artificial Magnets Artificial magnets are generally made of iron or steel in different convenient shapes. The different types of artificial magnets are : Types of magnet (i) Bar magnet : This is a bar of uniform cross-section, either rectangular or circular.

Figure N

S

S

N

A

B

(ii) Horseshoe magnet: This is a bar magnet bent in the shape of a horseshoe.

(iii)Needle magnet: This is a short thin strip of magnetised steel with pointed ends and pivoted at its centre.

S

N

(iv)Specially shaped magnets: These are for particular applications. Thus a loudspeaker magnet has a recess in it to accom­modate the coil. One design of extremely powerful magnet is as shown alongside.

(v)

Electromagnets: These can be the mostpowerful and are now a days used whenever a very intense magnetic field is required.

Drawbacks of Natural Magnets i) ii) iii)

Artificial magnets are far more strong than the natural magnets. The strength of the artificial magnets can be increased or decreased, while in the case of natural magnets it cannot be done. Artificial magnets can be made in any shape that suits our convenience, while natural magnets have irregular forms.

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6th Class Physics

80

Conceptive Worksheet

Formative Worksheet 1.

2.

3.

4.

5.

6.

7.

8.

One of the following is an artificial magnet (A) Horse shoe magnet (B) Magnetic needle (C) Magnetic compasses & electro magnet (D) Above all Assertion : Artificial magnets are preferred to natural magnets Reason : Artificial magnets are far stronger and can be cast in to any desired shape or size (A) Both Assertion and reason are correct (B) Both Assertion and reason are wrong (C) Assertion is wrong, Reason is correct (D) Assertion is correct, Reason is wrong Which one is appropriate : (A) The horse shoe magnet is more powerful than the bar magnet because both the north and the south poles face each other (B) Attractive force is doubled in horse shoe magnet. (A) Only A (B) Only B (C) Both A & B (D) None All Substances can be divided into _________ classes on the basis of their magnetic properties (A) 1 (B) 2 (C) 3 (D) 4 Which of the following cannot be magnetised? (A) Iron (B) Nickel (C) Cobalt (D) Stainless steel Copper, Gold are the examples of the following magnetic materials (A) Ferro (B) Dia (C) Para (D) Both A and B Which of the following is a not magnetic material (A) Nickel (B) Cobalt (D) Bismuth (D) Wood Statement-1: paper, wood, glass cannot be magnetized. Statement-2: Substance which are influenced or affected by a magnet is called a magnetic substance. (A) Statement-1 is true; Statement-2 is true; Statement-2 is the correct explanation of Statement-1 (B) Statement-1 is true; Statement-2 is true; Statement-2 is not the correct explanation of Statement-1 (C) Statement-1 is true; Statement-2 is false (D) Statement-1 is false; Statement-2 is true

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1.

2.

3.

4.

5.

6.

7.

Which of the following is a magnetic material (A) Wood (B) Plastic (C) Iron (D) Copper Deposits of magnetic oxide iron ore is called (A) Magnesia (B) Magnetic (C) Magnesite (D) Both (A) and (B) The first natural magnet is ____________ (A) Lode stone (B) Hard stone (C) Lime stone (D) None of these A piece of Iron rubbed with magnetite is called a (A) Magnet (B) Natural magnet (C) Artificial magnet (D) Iron ore Which of the following is employed for tracing magnetic lines of force of a magnet. (A) Load stone (B) Magnetic needle (C) Tracing compass (D) Bar magnet The following magnetic materials are very feebly attracted by a strong magnet (A) Para (B) Ferro (C) Dia (D) None Choose the correct example/s for the Ferro magnetic material. (A) Aluminum (B) Copper (C) Steel

(D) Cobalt

3. Properties of a Magnet 1.

2.

It attracts small pieces of iron towards itself It also attracts pieces of cobalt, nickel and steel. If a bar magnet is rolled in the iron filings, it is observed that iron filings cling at the ends of the magnet. However, no iron filings cling in the centre. This suggests that the magnetic force of attraction is concentrated near the ends of the magnet. A freely suspended magnet points in northsouth direction Take a bar magnet and suspend it freely from the centre by means of an unspun silk thread. It is observed that it points in the north-south direction. Even if we set the magnet in some other direction, it again resets itself in the north-south direction. The above property of magnet is used in the construction of magnetic compass. It must be noted that a freely suspended magnet does not really point in exact geographic north-south position, but is inclined at a slight angle to it.

Magnetism

81 suspended magnet is repelled, proving that the steel piece has been magnetized. Path of magnet

Permanent magnet

3.

4.

Like poles repel each other and the unlike poles attract each other Take two bar magnets. Suspend one of them freely 5. from an unspun silk thread. Bring the other magnet near it. You will see that, when the like poles of the magnets are brought near each other, they repel. If unlike poles are brought near each other, they attract each other .

This characteristic of the magnet is made use in determining the polarity of a magnet with the help of another magnet whose polarity is known. Repulsion is the surest test of magnetism. It is because the attraction can be caused between two unlike poles of the two magnets or between the magnet and the magnetic substances (such as iron, cobalt and nickel). How­ever, the repulsion is caused when two similar poles approach each other. Thus, repulsion is the surest test of magnetism. It can magnetize another piece of iron when rubbed several times in one direction) Take a steel bar AB and place it flat on the table. Rub this steel bar with a bar magnet as shown in figure for about 50 times. Test the end A of the steel bar by bringing it near the north pole of another freely suspended magnet. It is observed that the north pole of the freely

Steel bar

Magnetic poles exist in pairs If a bar magnet is broken into two equal parts, following observations are made: (i) Each part has attractive as well as directive property, i.e., each part is complete magnet, (ii) The magnetic strength of each part is half than that of the complete magnet, (iii) The new magnetic poles are formed where the cut is made on the magnet, (iv) The nature of magnetic polarity on a given cut is opposite to the polarity on the far end of the magnet. If the broken pieces are further broken, all the above mentioned observations are noticed till we reach molecular stage.

Conclusions 1. Magnetic poles exist in pairs. There cannot be a monopole. 2. Every molecule of a magnet is complete magnet by itself. 3. Overall attractive power of a magnet is equal to the sum total of attractive powers of molecular magnets.

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6th Class Physics

82 Magnet and Magnetic Substances

Magnet

Magnetic Substance

1. A substance which attracts metals like iron or steel and which always points in a particular direction when suspended freely is called a magnet. 2. A magnet has two poles, one of which is always directed towards the Geographic north and the other to the Geographic south when suspended freely.

1. Substances which are influe nced by a magnet are called magnetic substances. Iron, steel, nickel and cobalt are a few examples of magnetic substances. 2. A magnetic substance has no poles and does not point to any particular direction when suspended freely.

3. A pole of a magnet attracts the opposite pole and repels the similar pole of another magnet.

3. A magnetic substance is attracted both poles of a magnet.

by

4. General Definitions of Bar Magnet 1.

Pole: Each end of a bar magnet is called its pole.

2.

Geometric pole: The geometric end of a bar magnet is called its geometric pole. A

3.

B

A, B

Geometric poles

Magnetic Pole: The point situated slightly inside a bar magnet, where most of its magnetic power is concentrated is called its magnetic pole. A N N, S

Magnetic North pole The pole of a freely suspended bar magnet which point towards geographic north is called its magnetic north pole (N). X

N

S

B

Magnetic poles

Magnetic South pole The pole of a freely suspened bar magnet which points towards geographic south is called its magnetic south pole (S).

S

Y Magnetic axis (Axial line)

Magnetic Axis: An imaginary line joining the magnetic north and south poles of a bar magnetic is called its magnetic axis (or) axial line. (XY = magnetic axis) Equatorial Line: The line passing through the centre of magnet and perpendicular to the axial line is called equatorial line.

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Magnetism

83

Equatorial line

N

S

Magnetic Length: The distance between the two poles of a magnet is called magnetic length of magnet. Magnetic length

A

N

S

B

Geometric length

NS  Magnetic length AB = Geometric length The relation between magnetic length and geometric length is 5 MAGNETIC LENGTH   GEOMETRIC LENGTH 6

Magnetic Induction : The phenomenon due to which magnetism is produced in a magnetic substance by the mere presence of a magnet, which is not actually in physically contact with magnet is called magnetic induction. N

Demagnetisation :The loss of magnetic property of a magnet is called demagnetisation. By heating or by hammering or by rough handling, a magnet loses its property.

Formative Worksheet

S

Choose the correct statement/s from the following: (A) Magnetite can be called as lode store S Pin (B) Natural magnets possess attractive property N only S (C) Natural magnets possess attractive and Note: The end of an unmagnetised substance directional properties nearer to the pole of inducing magnet acquires opposite polarity, whereas the further end from (D) Natural magnets possess directional property inducing magnet acquires similar polarity. Magnetic only induction precedes magnetic attraction. 10. Statement-1: A freely suspended bar magnet Temporary Magnets: The magnets which lose always comes to lie in North-South direction. their magnetism as soon as the cause producing Statement-2 : Magnetic poles have the property of them is removed, are called temporary magnets. directionality Examples: Electromagnets and the magnets made (A) Statement-1 is true; Statement-2 is true; from soft iron are temporary magnets. Statement-2 is the correct explanation of ii) Permanent Magnets: The magnets which do Statement-1 not lose their magnetism, when the cause producing (B) Statement-1 is true; Statement-2 is true; them is removed, are called permanent magnets. Statement-2 is not the correct explanation of Examples: The magnets made from steel, cobalt Statement1 etc., are permanent magnets. (C) Statement-1 is true; Statement-2 is false Note: Soft iron is a temporary magnet whereas (D) Statement-1 is false; Statement-2 is true Steel is a permanent magnet. www.betoppers.com N

9.

6th Class Physics

84 11. Column – I A) Like poles of magnets B) Unlike poles of magnets C) Magnetic substance D) Non magnetic substance

Column – II p) Iron q) Repel r) Glass s) Nickel t) Attract

(A) A  p;B  q;C  r;D  s (B) A  q;B  t;C  p; D  r (C) A  q;B  s;C  p;D  t (D) A  p;B  p;C  q;D  p 12. A piece AB of the magnetite is dipped in a leap of small iron filings. It is observed that a cluster of iron filings stick to the ends A and B while there is practically no iron filing stick to its central region. Answer the following questions. (i) The central region or called (A) Neutral Region (B) Pole (C) Both A & B (D) Equator 14. Column – I A) The rest position of a magnet is B) Magnetic poles exist in pairs C) Iron is strongly attracted by magnet so it is D) Gold is repelled by a magnet so it is

(ii) End A is called (A) Neutral Region (C) Both A & B (iii) End B is called. (A) Neutral Region (C) Both A & B

(B) Pole (D) Equator (B) Pole (D) Equator

13. Statement-1 :Like poles attract each other Statement-2 : If a magnet is suspended freely, then the end marked with N points towards geographic north and the end marked with S points towards geographic south. (A) Statement-1 is true; Statement-2 is true; Statement-2 is the correct explanation of Statement-1 (B) Statement-1 is true; Statement-2 is true; Statement-2 is not the correct explanation of Statement1 (C) Statement-1 is true; Statement-2 is false (D) Statement-1 is false; Statement-2 is true Column – II p) Ferromagnetic substance along N-S when suspended q) Diamagnetic substance r) Directive property s) Dipole t) Paramagnetic substance

(A) A  p;B  q;C  r;D  s

(B) A  q;B  t;C  p; D  r

(C) A  q;B  s;C  p;D  t

(D) A  p;B  p;C  q;D  p

15. Magnetic poles exist in pair. We cannot get a magnetic monopole. When we cut a magnet, each piece will behave like a magnet with two poles.

Based on the above, answer the following Questions. (i) A bar magnet is cut as shown in the figure. Mark the polarity of each pole (from left to right) for the polarity missed piece.

(A) South, North

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(B) North, South

(C) North, North

(D) South, South

Magnetism

85

(ii) A bar magnet is cut as shown in the figure. Mark the polarity of each pole (from left to right) for polarity missed piece.

(A) South, North (B) North, South (iii) A bar magnet is cut as shown in the figure.

(C) North, North

(D) South, South

Match the following for the polarity. LIST – I LIST– II a) 1,2 e) South, North b) 3,4 f) North, South c) 5,6 d) 7,8 (A) a–e, b–e, c–f, d–f

(B) a–f, b–f, c–e, d–e

(C) a–f, b–f, c–e, d–e

(D) a–f, b–e, c–f, d–e

16. Statement A: The more is the distance of the magnetic substance from the magnet, the weaker is this attraction. Statement B: Magnet can attract magnetic substances within the magnetic field (A) Both the statements are true (B) Both the statements are false (C) Only statement A is true (D) Only statement B is true 17. Statement A: The points of the magnet where there is maximum attraction are called the poles of the magnet Statement B: Magnetic poles always exist in pairs (A) Both the statements are true (B) Both the statements are false (C) Only statement A is true (D) Only statement B is true 18. Magnetic length of a bar magnet is nearly 80% of its geometric length. If a magnet has a geometric length of 12cm. Answer the following: (i)

Find its magnetic length. (A) 9.6 cm

(B) 24 cm

(C) 15 cm

(D) 12 cm

(ii) The difference between geometric length and magnetic length is (A) 0 cm

(B) 3 cm

(C) 12 cm

(D) 2.4 cm

(iii) How much percentage does the magnetic length is small when compare to geometric length. (A) 25 %

(B) 50 %

(C) 20 %

(D) 100 %

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6th Class Physics

86

Conceptive Worksheet 8.

9.

10.

11.

12.

13.

14.

15.

16. 17.

18.

One of the following is not a property of a magnet (A) Attraction (B) Repulsion (C) Induction (D) Reflection When magnet is suspended freely, then the end marked N, points towards (A) Geographic North (B) Geographic South (C) We can’t say (D) Depends on magnet Which of the following is the property of a magnet? (A) Pair property (B) Directionality (C) Like poles repel & unlike poles attract (D) All the above A vertical plane passing through the magnetic axis of a freely suspended magnet (A) Magnetic Meridian (B) Magnetic equator (C) Equatorial Meridian (D) Magnetic Pole A vertical plane passing through the magnetic equator of a freely suspended bar magnet is called (A) Magnetic Pole (B) Magnetic equator (C) Equatorial Meridian (D) Magnetic Meridian If the length of the magnet is l, then the effective length of the magnet is (A) 4l (B) 3l (C) l (D) 2l The magnetic strength or magnetic intensity is maximum at the __________ of a bar magnet (A) Pole (B) At its centre (C) Equatorial line (D) Axial line The regions of concentrated magnetic strength inside the magnet just near its ends are called magnetic ________________. (A) Pole (B) Axis (C) Meridian (D) Length The region or the space surrounding a magnet in which magnetic force is exerted is called the ____ The attraction of iron filings in a magnet is maximum at (A) Poles of the magnet (B) Middle part of the magnet (C) All places in the magnet (D) None of these Pole strength does not depend on (A) Length of a magnet (B) Breadth of a magnet (C) Height of the magnet (D) Both (B) and (C)

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19. The relation between a magnetic field at a point and the distance between a magnet and at a point is (A) Inversely proportional to the square of the distance (B) Inversely proportional to distance (C) Directly proportional to the square of the distance (D) None of these

Summative Worksheet 1.

A magnetic needle is suspended from a stand near north pole of the earth it aligns itself (A) Horizontal (B) Vertical (C) Inclined 45° to the vertical 0

1 to the vertical 2 You have a magnet with you and north pole and south pole are marked on it. There is a bar on a table. To find out whether it is a magnet or a magnetic substance, which one is the sure test ? (A) Repulsion (B) Attraction (C) Both attraction and repulsion (D) None For making electromagnets _____ material is used. (A) Aluminium (B) Steel (C) Soft iron (D) Copper Select the correct statement(s): (A) South pole attracts south pole (B) North pole attracts north pole (C) North and south poles cannot be separated (D) Artificial magnets are more powerful than natural magnets When a magnet is heated, it (A) Loses its magnetism (B) Gains magnetism (C) Gains magnetism up to a certain temperature and loses magnetism beyond that temperature (D) Neither gains nor loses magnetism

(D) Inclined 22 2.

3.

4.

5.

Magnetism 6.

7.

8.

9.

10. 11. 12. 13. 14. 15. 16.

87

Demagnetisation of a magnet can be done by (A) Rough handling (B) Heating (C) Magnetising in the opposite direction (D) All the above A small piece of an unmagnetised material gets repelled when it is brought near a powerful magnet. The material is (A) Paramagnetic (B) Diamagnetic (C) Ferromagnetic (D) Non-magnetic If a piece of metal was thought to be a magnet, which one of the following observations would offer conclusive evidence ? (A) It attracts a known magnet (B) It repels a known magnet (C) It attracts a steel screw driver (D) None of above An example for diamagnetic substance is (A) Copper (B) Iron (C) Nickel (D) Aluminium A freely suspended magnet points towards geographical north and south; this property is ? The surest test of magnetism is___ ? An Electromagnet is ___ ? Attractive property of magnet is more at ? The North pole of earth’s magnet is near the geographical ? Name some magnetic material ? When a magnet is broken as shown. The poles at

‘X’ and ‘Y’ are

1.

A

?

The relation between geometric length and magnetic length of a bar magnet is given by

5 × Geometric length. 6 If the difference between geometric length and magnetic length of a bar magnet is ‘K’ units, then find its geometric length and magnetic length. The strength of a magnetic pole is measured in terms of pole strength. Pole strength depends on number of free poles exposed at the end of the magnet. Number of free poles exposed at the end of magnet inturn depends on the area of cross section of the magnet. A bar magnet has a pole strength ‘K’. If is cut into 2007 parts as shown in the figure. The pole strength of each piece now is _____ Magnetic length =

2.

(A) 2007K 3.

4.

?

17. Permanent magnets behave like a magnet even after ___ ? 18. Which of the following is property of a magnet ? 19. The spring in the case extend large when magnet

‘B’ is ___

HOTS Worksheet

5.

(B)

K (C) K 2007

(D) K+2007

A bar magnet has a pole strength ‘K’. If it is cut into 4 pieces as shown in the figure. The pole strength of each piece now is __________.

K K (C) 4K (D) 4 2 A bar magnet of dimensions l, b and h has pole strength of K units. Now its dimensions are doubled. The new pole strength is _______. (A) K + 4

(B)

(A) K+ 4

(B) K–4 (C) 4K

(D)

K 4

The product of the length of the magnet and its pole strength is called the moment of a magnet or Magnetic moment. If ‘m’ is the pole strength and 2l is the length of the magnet then, the moment of the magnet or Magnetic moment is given by. M = m×2l. Also, Magnetic moment is a vector quantity, with its direction from south pole to north pole along its axial line. If a bar magnet of magnetic moment 80 units be cut into two halves of equal lengths, the magnetic moment of each half will be (A) 80 units (B) 60 units (C) 40 units (D) 20 units www.betoppers.com

6th Class Physics

88

___ is the suitable material for cor e of electromagnet (A) Steel (B) Copper (C) Soft Iron (D) Ceramic 7. In which of the following, permanent magnet is used (A) Electric Bell (B) Loudspeaker (C) Compass Needle (D) Electric Motor When South (S) pole of magnet is placed near an unknown pole of another magnet. The two magnets (A) Repel each other when the unknown pole is 8. N - pole (B) Attract each other when the unknown pole is N - pole (C) Attract each other when the unknown pole is S - pole (D) None M (B) Magnetic moment 7. Natural Magnet is known as 4 (A) Magnetite (B) Lodestone M (C) Magnetic moment (C) Both (D) None 2 8. Which of the following is not correct ? (D) Magnetic moment M –1 2 (A) The north pole of a magnet attracts south pole 9. The moment of a magnet is 3 × 10 Am and the of another magnet length of the magnet is 10cm. The pole strength of the magnet is (in A.m) (B) Isolated magnetic poles do not exist (A) 30 (B) 60 (C) 3 (D) 6 (C) Artificial magnets are made from magnetic materials 10. A magnetised straight wire has a magnetic moment M. If it is bent into a semicircle its magnetic moment (D) None will be 9. Magnetism by electric current method is ___ than other methods M M 2M (A) M (B)  (C) 2 (D)  (A) More Strong (B) Strong (C) Weak (D) Very Weak orksheet 10. A weak magnet brought near a strong magnet with I. Single Correct Answer Type same poles facing each there, then 1. If a bar magnet is cut into 4 pieces. Each piece is (A) Both will repel (A) Individual Magnet (B) Weaker magnet will move away (C) Stronger magnet will move away (B) Some pieces have only North Pole (D) Initially there is repulsion then strong magnet (C) Some pieces have only South Pole will attract the weak magnet (D) All pieces lose magnetism 11. When two substances repel each other then 2. Surest test of magnetism is (A) One of them must be a magnet (A) Attraction (B) Repulsion (B) Both of them must be magnets (C) Both Repulsion and Attraction (D) None (C) One of them must be non magnetic 3. Compass is used (D) Both of them must be non-magnetic (A) To find direction on sea and earth (B) To attract magnetic material (C) Alignment along N-S direction (D) Options 1and 3 both 6.

A bar magnet of magnetic moment M is cut into 4. four parts of equal length. The magnetic moment of either part is (A) M (B) 4M (C) M/4 (D) Zero A magnetic needle of magnetic moment M and pole 5. strength m is broken into two pieces at the middle. The magnetic moment and pole strength of each piece will be 6. M m m M , , m (D) M, m (A) (B) m, (C) 2 2 2 2 Two similar bar magnets P and Q, each of magnetic moment M, are taken. If P is cut along its axial and Q is cut along its equatorial line, all the four pieces obtained have (A) Equal pole strength

IIT JEE W

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Magnetism 12. After repeated rubbing with a magnet in the same direction. The substance fails to get magnetised it should be a (A) Magnet (B) Non-Magnetic substance (C) Magnetic Substance (D) All the above 13. A bar of steel can be permanently magnetised by (A) Rubbing with a bar magnet at its center (B) Rubbing with a bar magnet at its ends (C) Rubbing with a bar magnet along its length (D) None 14. Strength of the magnet depends on (A) Length of the magnet (B) Size of the magnet (C) Both (D) None 15. When one end of a magnet is placed near a compass pointer. The pointer (N - pole) of a compass turns away because (A) The end of a magnet near the pointer of compass is N-pole (B) The end of a magnet near the pointer of compass is S-pole (C) Both (D) None 16. Magnetic field around a magnet is (A) One dimensional (B) Two dimensional (C) Three dimensional (D) None 17. Earth magnetic field is studied under the name (A) Terrestrial Magnetism (B) Plant’s Magnetism (C) Earth’s Magnetism (D) None 18. Nature of magnetic force is (A) Attraction (B) Repulsion (C) Either attraction or repulsion (D) Neither attraction nor repulsion 19. Geometric length of magnet is equal to ___ its magnetic length

5 6 2 3 times (B) times (C) times (D) times 6 5 3 2 20. The direction in which a magnet points at a place on earth (A) Changes (B) Do not change (C) We cannot say (D) None (A)

89 II.

Multiple Correct Answer Type

21. An imaginary line joining the magnetic north and south pole of a bar magnet is its (A) Magnetic axis (B) Axial line (C) Equitorial line (D) Pole 22. A magnet can be demagnetised by (A) Heating (B) Hammering (C) Rough handling (D) Induction 23. Which of the following are made as permanent magnets (A) Steel (B) Cobalt (C) Soft iron (D) Iron 24. Choose the correct statement/s from the following: (A) A freely suspended magnet points in N-S direction (B) Magnetic poles exist in pairs (dipole) (C) A freely suspended magnet points in E-W direction (D) Magnetic poles does not exist in pairs 25. Which of the following are diamagnetic substances? (A) Phosphorus (B) Water (C) Antimony (D) Platinum

III. Paragraph Type Paragraph-1 A piece AB of the magnetite is dipped in a leap of small iron filings. It is observed that a cluster of iron filings stick to the ends A and B while there is practically no iron filing stick to its central region. 26. The central region or called (A) Neutral Region (B) Pole (C) Equator (D) none of these 27. End A is called (A) Neutral Region (C) Equator

(B) Pole (D) none of these

28. End B is called. (A) Neutral Region (C) Equator

(B) Pole (D) none of these

Paragraph-2 The force of attraction between two point magnetic poles is directly proportional to the product of their pole strengths and inversely proportional to the square of the distance between them.

m1m 2 Km1m 2  F 2 d d2 Where K is a constant, m1 and m2 are pole strengths i.e. F 

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6th Class Physics

90

and ‘d’ is the distance between them. This is called 32. Do you think the force between two poles depends Coulomb’s law. on medium in which they are present Using the above information, answer the following (A) Yes (B) No questions. (C) Sometimes yes and sometimes no 29. The force between two poles (m1 and m2) in air (D) Cannot be predicted which are separated by a distance ‘d’ is F. If the distance is doubled, the force between the poles in 33. Find the force exerted on a point north pole of strength 3200amp-m placed 10cm away in air from air now is ________. a point south pole of strength 40amu.m F F (A) 4F (B) 2F (C) (D) (A) 1N (B) 1.28N (C) 2N (D) None 2 4 30. The force between two poles (m1 and m2) in air IV. Integer Type which are separated by a distance ‘d’ is F. If m1 is 34. All substances can be divided into _________ halved and m2 is doubled and the distance is same classes on the basis of their magnetic properties i.e., d, the force now is ___ 35. The relation between magnetic length and geometric F 1 (A) F (B) (C) (D) 4F x 2 F length is Magnetic length =  Geometric length 6 31. When the distance between two magnetic poles is halved, the force between them will become ,then the value of x is ___ (A) Halved (B) One fourth (C) Doubled (D) Four times

V. Matrix Matching 36. (A) Naturally occurring magnet (B) The end of freely suspended magnet moved towards north (C) Device used for finding geographic directions

(p) Magnetic substances (q) Magnetite (r) Non - Magnetic (s) Compass needle (t) N - pole

37. (A) Similar poles of magnet (B) Opposite poles of magnet (C) Horse shoe magnet (D) Electromagnet

(p) Lodestone (q) Artificial magnet (r) Strong magnet (s) Attract (t) Repel

38. (A) Temporary Magnets (B) Permanent Magnets

(p) Compass Needle (q) Television, loudspeaker, electric cranes, motors (r) Planet’s Magnetism (s) Terrestrial Magnetism

(C) Earths Magnetic Field

39. (i) Soft Iron (ii) Alnico, steel, ceramics (iii) Ironoxide

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(a) Loadstone (b) For Electromagnets (c) For Permanent Magnets (d) Artificial Magnets

B y t h e e n d o f t h i s c h a p t e r , yo u w i l l un de r s t an d • • • • •

Heat Sources of Heat Effects of Heat Temperature Expansion of substances

• • • • •

Transmission of heat Conduction Convection Radiation Conductors and insulators

1. Introduction Heat is a form of energy. Heat produces a sensation in our body by which we make out whether a body is cold, warm or hot. A hot body has more of heat energy in it than a cold body. Hotness or coldness of any object can be known through its ‘heat’. Direction of the flow of heat is from hot to cold. Measure of heat is Temperature. Hotness or Coldness are only relative. The total amount of heat energy is called Enthalpy.

2. Sources of heat Sun Is the ultimate source of heat energy. Plants absorb sunlight and manufacture starch and sugars through a process called ‘Photosynthesis’. Other Sources of Heat Wood, Coal, Cooking gas, burning candle produce heat when they burn. Heat is also produced: When work is done against friction. When fuels are burnt.

3. Temperature The degree of hotness or coldness of a body is called temperature. Heat is cause which makes temperature take its effect. Units of Heat and Temperature S.I unit of heat is Joule. Other unit of heat is Calorie. S.I unit of temperature is Kelvin. Other units are Degree Centigrade(oC), Degree Fahrenheit(oF). Centigrade is also called Celsius.

Chapter -37

Heat

Learning Outcomes

4. Effects of Heat Heat gives the capacity to do work. Substances expands on heating. Heat changes the state of substance. Air when heated become lighter. Micro-organisms in liquids like milk are destroyed on heating. Hen’s incubation supplies heat to the eggs which help them transform into chicks.

5. Effect of Heat on the size of the substances All matter expands on heating Solids expand on heating. Substances expand on heating; this expansion is different for different substances. Liquids expand on heating. Different liquids have different rates of expansion for the same rise in temperature. Gases also expand on heating. Expansion in gases is very large as compared to the solids or liquids.

6. Transmission of Heat Heat transfer from hotter objects to colder objects. Heat is transferred from hot end to cold end by 3 methods, namely: Conduction Convection Radiation Conduction Transfer of heat without actual movement of the particles of the medium is called conduction. It occurs only in solids. Convection Transfer of heat through the movement of particles of the medium from one place to another is called convection. It occurs in liquids and gases (fluids). Radiation The transfer of heat without any medium from one place to another is called radiation Eg: Heat from the sun passes through the vacuum

6th Class Physics

92 in the space where there is nothing (neither any solid nor any fluid) Based on the transfer of heat, substances are categorised into: Insulators and Conductors Insulators Substances which do not allow heat to pass through them are called insulators. Ex: Paper, rubber, wood, all fluids except mercury are poor conductors of heat. Conductors Substances which allow heat to pass through them are called conductors. Ex: Copper, Iron, Aluminium, Silver, Lead.

8.

9.

10.

Formative W orksheet 1.

2.

3.

4.

5.

6.

7.

Which sense in our body helps in distinguishing cold, warm and hot body? (A) Sense of Smell (B) Sense of Touch (C) Sense of Vision (D) Sense of Hearing Which of the following is the effect of heat energy ? (A) Change in Temperature (B) Change in the State (C) Chemical Change (D) All S.I. Unit of temperature is ___ ? (A) Celsius (B) Fahrenheit (C) Kelvin (D) None Fastest mode of transmission of heat is ? (A) Conduction (B) Convection (C) Radiation (D) None Black surfaces are ? (A) Good absorbers of heat (B) Good radiators of heat (C) Poor absorbers of heat (D) Good absorbers and good radiators of heat A bimetallic strip is made of copper and iron when heated in a flame ? (A) Iron expands more and bends on copper strip (B) Copper expands more and bends on iron strip (C) Both iron and copper expand equally (D) None A wooden spoon is dipped in a cup of ice cream; its other end ? (A) Becomes cold by the process of conduction (B) Becomes cold by the process of convection (C) Becomes cold by the process of radiation (D) Does not become cold

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11.

12.

13.

14.

Stainless steel pans are usually provided with copper bottoms. The reason for this could be that ? (A) Copper bottom makes the pan more durable (B) Such pans appear colourful (C) Copper is better conductor of heat than the stainless steel (D) Copper is easier to clean than the stainless steel Device in which heat losses are minimised due to conduction, convection and radiation is ? (A) Thermometer (B) Bimetallic Strip (C) Thermos flask (D) Solar Cooker Which of the following is arranged in decreasing order of conductivity of heat inmetals ? (A) Lead, Silver, Al, Iron, Copper (B) Silver, Copper, Al, Iron, Lead (C) Copper, Silver, Iron, Lead, Al (D) Silver, Copper, Al, Lead, Iron (i) Temperature (a) Energy (ii) Heat (b) 0oC - 100oC (c) Force (iii) Centigrade Scale (d) Measurement of Energy (A) i - c, ii - a, iii - b (B) i - d, ii - a, iii - b (C) i - a, ii - b, iii - c (D) i - b, ii - c, iii - d (i) Silver, Copper, Lead, Iron (a) Solids (ii) Wood, Wool, Bakelite, Plastics (b) Fluids (iii) Convection (c) Conductors (d) Insulators (A) i - b ii - c iii - d (B) i - a ii - b iii - c (C) i - c ii - d iii - b (D) i - d ii - a iii - b (i) Process due to which a solid directly change into gaseous state temperature (a) To measure very low (ii) Alcohol thermometer (b) Sublimation (iii) Liquid metal (c) To measure high temperature (A) i - b ii - a iii - c (B) i - a ii - c iii - e (C) i - b ii - c iii - d (D) i - c ii - d iii - e (i) Land breeze blows during (a) Summer (ii) Sea breeze blows during (b) Winter (iii) Dark colour clothes are preferred during (c) day (d) Night (A) i - a ii - b iii - c (B) i - b ii - c iii - d (C) i - c ii - d iii - a (D) i - d ii - c iii - b

Heat

Conceptive W orksheet 1.

2.

3.

4.

5.

6.

7.

8.

Which body feels hot ? (A) A body losing heat (B) A body gaining heat (C) Both (D) None Under what condition the flow of heat is rapid? (A) One of the two bodies is too hot (B) One of the two bodies is too cold (C) There is a big difference in the temperature of two bodies (D) All ___ is the physical quantity which measures the amount of heat in a body ? (A) Temperature (B) Energy (C) Mass (D) None o One litre of water at 30 C is mixed with one litre of water at 60oC, the temperature of the mixture will be ? (A) 90oC (B) More than 60oC but less than 90oC (C) 30oC (D) Between 30oC & 60oC A steel cup at 400oC is dropped in a container of water at 40oC, then? (A) Heat will flow from cup to water (B) Heat will not flow from cup to water or from water to cup (C) Heat flow from water to cup (D) The temperature of cup increases Normal temperature of human body is ? (A) 37oC (B) 98.4oF (C) Both (D) None Which of the following is NOT correct in ‘heattransmission through conduction’ ? (A) Heat flows only when one end of an object is hot and other end is cold. (B) When heat is flowing through two objects they must remain in contact with one another. (C) Once the two ends of the object through which heat is flowing attain the same temperature conduction of heat stops. (D) In conduction, heat is transferred through the moving particles of medium from one place to another. Heat transmission through convection does not take place in ___? (A) Liquids (B) Gases (C) Solids (D) None

93 9.

While sitting near a heater or a bonfire, you feel warm. The heat from the heater reaches you by _____ process? (A) Conduction (B) Radiation (C) Convection (D) All 10. Handles of electrical appliances and cooking utensils are made from ? (A) Bakelite (B) Plastics (C) Wood (D) All

Summative W orksheet 1.

Why do we feel hot when we shift our hand from a bowl of cold water to a bowl of tap water? 2. Thermometer is a ___? 3. Practical uses of good conductors of heat ? 4. Why refrigerators have double walled body ? 5. All fluids expects mercury are ___ of ? 6. Two thin woolen blankets are warmer than a thick woolen blanket ? 7. Ventilators are the application of ___? 8. Amount heat energy transmitted by mean of radiation is ___? 9. Why we make use of glass panes on our doors and windows ? 10. By the process of convection, the heart transmission is always ___ ?

HOTS W orksheet 1.

2.

3.

Fill in the blanks with the correct words. (A). The degree of hotness or coldness of a body is called ___________. (B) Heat is a form of ____________. (C) Heat energy is measured in _______. Write true or false. (A) Temperature is a form of energy. (B) Heat energy flows from a hot body to a cold body. (C) Temperature is measured in joules. (D) When heat energy flows into a body it warms the body. Heat energy will flow from our body to the surroundings if (A) The surroundings are at a higher temperature than our body. (B) The surroundings are at the same temperature as our body. (C) The surroundings are at a lower temperature than our body. (D) There is no relationship between heat flow and temperature. www.betoppers.com

6th Class Physics

94 4.

Define the following: (A) Conduction (B) Convection (C) Radiation 5. Conduction, convection, and radiation are (A) Different modes of heat energy (B) Different modes of heat transfer (C) Different measures of temperature (D) All of these 6. Convection does not occur in (A) vacuum (B) liquids (C) gases (D) air 7. Which of these is a good conductor of heat? (A) Wood (B) Straw (C) Water (D) Copper 8. Which of these is a bad conductor of heat? (A) Wool (B) Gold (C) Copper (D) Stainless steel 9. Name the mode of heat transfer in each of the following cases: (A) In a vessel of boiling water. (B) Heat energy reaching us from the sun. (C) A vessel kept on a hot stove becomes hot. (D) Warm breeze from the land flows towards the sea. (E) A spoon kept in a hot tea cup becomes warm. 10. (A) Name the mode of heat transfer from one body to another where it is essential for the two bodies to be in contact. (B) Name the mode of heat transfer that can take place even in vacuum.

5.

II. Multiple Correct Answer Type 6.

7. 8. 9.

Temperature is the measure of hotness or coldness of a body. Temperature is measured in both Celsius (°C) and Fahrenheit scales (°F). Conversion Formula Two simple equations given below will help us to scale convert one temperature scale to another.

Single Correct Answer Type

The S.I. Unit of temperature is : (A) Celsius (B) Fahrenheit (C) Kelvin (D) None 2. Fastest mode of transmission of heat is ? (A) Conduction (B) Convection (C) Radiation (D) None 3. A wooden spoon is dipped in a cup of ice cream; its other end ? (A) Becomes cold by the process of conduction (B) Becomes cold by the process of convection (C) Becomes cold by the process of radiation (D) Does not become cold 4. One litre of water at 30oC is mixed with one litre of water at 60oC, the temperature of the mixture will be ? (A) 90oC (B) More than 60oC but less than 90oC (C) 30oC (D) Between 30oC & 60oC www.betoppers.com

Which of the following is the mode of heat transfer? (A) Conduction (B) Convection (C) Radiation (D) Radioactivity Which of the following is a form of energy? (A) Heat (B) Sound(C) Light (D) Electricity Which of the following is the unit of heat energy? (A) Joule (B) Calorie (C) Metre (D) Second Which of the following is the effectof Heat? (A) Heat gives the capacity to do work. (B) Substances expands on heating. (C) Heat changes the state of substance. (D) Micro-organisms in liquids like milk are destroyed on heating.

III. Paragraph Type

IIT JEE W orksheet I.

A steel cup at 400oC is dropped in a container of water at 40oC, then? (A) Heat will flow from cup to water (B) Heat will not flow from cup to water or from water to cup (C) Heat flow from water to cup (D) The temperature of cup increases

1.

10.

11.

12. 13.

9  F =  C×  + 32 5  5 C =  F  32  where F is for Fahrenheit and C is 9 for Celsius. Based on this information answer the questions given below. The body temperature of an animal is 86 °F. Express the same temperature in degree Celsius. (A) 120 °C (B) 90°C (C) 60°C (D) 30° The day temperature in Delhi on a hot day was 45 °C. Express this temperature in degree Fahrenheit. (A) 113 °C (B) 103 °F (C) 93 °F (D) 83 °F Express 35 °C in Fahrenheit scale. (A) 75 °F (B) 85 °F (C) 95 °F (D) 105 °F Express 41 °F in Celsius scale. (A) 10°C (B) 5°C (C) 20°C (D) 35 °C

IV. Integer Type 14. The melting point of ice = _______°C 15 Heat is transferred from hot end to cold end by ________ methods.

Heat

95

V. Matrix Matching (Match the following) 16. Match the following. Column – I Column – II (A) Insulator p. Unit of heat energy (B) Energy q. Good conductors (C) Fahrenheit r. Rubber (D) Joule s. Thermometer (E) Metals t. Heat 16. Match the following Column – I Column – II (A) Temperature (p) Energy (B) Heat (q) 0oC - 100oC (r) Force (C) Centigrade Scale (s) Measurement of Energy 17. Match the following Column – I Column – II (A) Silver, Copper, Lead, Iron (p) Solids (B) Wood, Wool, Bakelite, Plastics (q) Fluids (C) Convection (r) Conductors (s) Insulators 18. Match the following Column – I Column – II (P) Land breeze blows during (p) Summer (Q) Sea breeze blows during (q) Winter (R) Dark colour clothes are preferred during (r) day (s) Night

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IIT FOUNDATION Class VI

PHYSICS SOLUTIONS

© USN Edutech Private Limited The moral rights of the author’s have been asserted. This Workbook is for personal and non-commercial use only and must not be sold, lent, hired or given to anyone else.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior written permission of USN Edutech Private Limited. Any breach will entail legal action and prosecution without further notice.

Utmost care and attention to the details is taken while editing and printing this book. However, USN Edutech Private Limited and the Publisher do not take any legal responsibility for any errors or misrepresentations that might have crept in.

Published by

:

USN Eductech Private Limited Hyderabad, India.

CONTENTS 1.

Measurement

..........

096 - 101

2.

Motion and Force

..........

102 - 105

3.

Energy and Work

..........

106 - 111

4.

Light

..........

112 - 117

5.

Electricity

..........

118 - 123

6.

Magnetism

..........

124 - 124

7.

Heat

..........

125 - 126

6th Class Physics

96

1. MEASUREMENT SOLUTIONS

FORMATIVE WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

11

12

Ans

C

A

A

D

D

C

A

D

B

D

B

C

Q.no

13

14

15

16

17

18

19

20

21

22

23

24

Ans

A

*

*

C

D

B

C

A

B

B

D

C

Q.no

25

26

27

28

29

30

31

32

Ans

A

B

C

C

D

C

A

B

* Indicates the subjective questions

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1. 2. 3. 4. 5. 6.

8. 9.

10. 11. 12.

13. 14.

Both standard instruments and units are needed to measure physical quantities accurately. Measurement has two parts. They are number and unit. The standard used to measure a certain Physical quantity is called the unit. Pace or a footstep is a Non standard unit of length Cubit is a non standard unit and 10 kilometre = 10× 1000 metre. Statement I is false ; Statement II is true. The fundamental quantites are length, mass and time. M.K.S system is also named as S. I. System.

15. (A) 1 decametre = 10 m 1 decimetre = 10–1 m 

 1 decametre = 100 decimetre (B) 1 millimetre = 10–3 m 1 centimetre = 10–2 m 

  (D)

Diametre 

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1milli metre 103 = =103 ×102 =101 =0.1 1centi metre 102

 1 millimetre = 0.1 centimetre (C) 1 hecto = 102 m 1 kilometre = 103 m

1 km = 103 m ; 1 m = 100 cm ; 1 cm = 10 mm 1 km > 1 m > 1 cm > 1 mm

4.8  0.2 cm 24 1 km = 1000 m 3250 m = 3.25 × 10 m = 3.25 km 1 mm = 10–3 m (or) 1 m = 1000 mm 1.65 m = 1.65 × 103 mm = 1650 mm  The diameter of spherical object = x2 – x1 = 4.7 – 3.4 = 1.3 cm (A) 1 cm = 10 mm (B) 1 dm = 10 metre. (C) 1 kilometre = 1000 metre. (D) 1 metre = 100 centimetre.

1deca metre 10 = =10×10=100 1deci metre 10-1

 

16. 17. 18.

1hecto metre 102 = =102 ×103 =101  0.1 1kilo metre 103

1 hectometre = 0.1 kilometre. 1 decimetre = 10–1 m 1 centimetre. = 10–2 m 1deci metre 101 = =101×102 =10 1centi metre 102 1 decimetre = 10 centimetre.

A = 6×5 = 30 cm2. A = 450 × 145 = 65250m2 = 6.525 × 104 m2 = 6.525 hectare (  1 hectare = 104 m2)  Note: The option B, in the questions should be changed to x = 10–4, y = 10–2, z = 10–12

Measurement Solutions a) 1 hectare = 104m2  1m2 = 10–4 hectare b) 1 hectare = 104 m2 = 104 × (10–3 km)2 = 104 × 10–6 km2 = 10–2 km2 c) 1mm =10–3m. = 10–3 ×10–3km  1 mm2 = (10–6 km)2 = 10–12 km2 19. A = 20 × 12 = 240m2 20. V = 5× 4 × 3 = 60cm3 21. Volume of stone = 125 – 75 = 50 cm3 22. Final volume = 80 + 50 = 130 cm3 23. V = lbh 12 = 3× 2 × h

h 24.

25. 26.

97 27.

= 5000 mm3 1 Quintal = 100 kg 1ton = 1000 kg



1 Quintal 100 kg  1 ton 1000 kg

1 Quintal = 10–1 ton = 0.1 ton 1 metric tonne = 1000 kg 1 milligram = 10–3 g

 28.



1 metric tonne 1000 kg  1 milligram 103 g 

12  2cm 6

Dimensions = 0.003 km × 0.03m × 3m If we see options, it is clear that answer is expressed in cm3. so we need to express all the units in terms cm. 0.003 km = 0.003 × 1000m = 0.003 × 1000 ×100 cm = 300 cm 0.03m = 0.03 × 100 cm = 3 cm  V = 300 × 3 × 3 = 2700 cm3 Initial volume = 9.3 – 5.8 = 3.5 ml 5 cm3 = –––––– (mm)3 1 cm = 10mm.  5cm3 = 5×(10 mm)3 = 5 ×103 mm3

29.

= 106 ×103 g = 109  1 metric tonne = 109 milligram 1 microsecond = 10–6 s 1 milli second = 10–3 s



30. 31.

32.

1000  1000 g 103 g

1 microsecond 10 6 s  1 milli second 103 s

 1 micro second = 10–3 millisecond  x=–3 1 kg = 10–3 tonne. 1 tonne = 1000 kg. 4.4 tonnes = 4.4 × 103 kg. = 4400 kg 6 × 60 × 60 + 8 × 60 = 22080 sec.

CONCEPTIVE WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

11

12

Ans

A

B

D

D

A

C

C

C

D

A

C

A

Q.no

13

14

15

16

17

18

19

20

21

22

23

24

Ans

D

C

B

A

A

C

C

A

B

A

B

C

Q.no

25

26

27

28

29

30

31

32

33

34

35

36

Ans

B

B

B

A

A

A

B

C

A

A

C

A,C

Q.no

37

38

39

Ans

A

A

D

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6th Class Physics

98

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1.

2.

3. 4. 5. 6. 7. 8. 9.

10. 11. 12. 13. 14.

19.

Length is the fundametal quantity. Metre, Yard and Cubits are the different units of length. Number of fundamental physical quantities in M.K.S system three. They are length, mass and time. Cubit is a non standard unit of length Metre is the MKS unit of length. F.P.S stands for Foot, pound, second . C.G.S stands Centimetre, gram, second C Micro = 10–6 Centimetre is the unit of length. Whereas milli, kilo and micro are the prefixes used for different of units of measurement. Metre 4 kilometre = 4×103 metre. 15 cm = 15×10 mm ( 1cm = 10 mm) = 150 mm All the given relations are correct. 1 cm = –––––– km. 1 cm = 10–2 m. 1 km = 103 m.

100  100 1

25. 26. 27. 28.

29. 30.

31.

 1 cm = 10–5 km. 1 mm < 1 cm < 1 m < 1km 1 Angstrom = 10–8 cm (or) 10–10 m 1 AU = 1.496 ×1011 m 1 km = _________ microns. 1 km = 103 m. 1 micron = 10–6m.



21. 22. 23. 24.

1cm 102m   3  105 1km 10 m 15. 16. 17. 18.

20.

Least count of metre scale 1mm = 0.1 cm 1 cm2 = _______ mm2. 1 cm = 1× (10mm)2 = 100 mm2

32. 33. 34. 35. 36. 37. 38. 39.

1km 103 m  1m 106 m

 1km = 109  m.

Graph paper Unit of Area 1 hectare = 104m2 = 104 (10–3 km)2 = 104 × 10–6 km2 = 10–3 km2  1 km2 = 100 hectare 1 hectare = 104 m2 B m3 1m3 = ––––––––– cc 1m3 = 1 × (102cm)3 = 1 × 106cm3  1m3 = 106 cc A 1 litre = 1000 ml = 1000 cm3 = 1000 × (10–2 m)3 = 1000 × 10–6 m3  1 litre = 10–3 m3 The space occupied by a substance is called volume. Cubic metre 1 m3 = 106 cc V = l3 = 1 cm × 1 cm × 1cm = 1cc 1 mean solar day = 24 hours. (A) 51 cm of cloth (C) Surface Area = 40 cm2 1 Quantal = 100 kg 12O’clock at night 18 hours  18 – 12 = 6 hours Time = 6 hours 15 minutes 

SUMM ATIVE WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

Ans

D

A, B

A

A

D

D

B

C

A

C

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Measurement Solutions

99

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1. 5.

Both thread and scale are required to measure a curved line. 1 cm2 = 1 ×(10–2m)2 = 10–4 m2 = 10–4 × (10–3 km)2 = 10–10 km2 = 10–8 hectare. 1 hectare = 104 m2  1m2 = 10–4 hectare = 10–6 km2 = 10–2 acre

6.

HOTS WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

11

12

Ans

B

B

B

A

D

C

B

A

D

C

A

D

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1.

2.

3.

4.

5.

V = 12 ml = 12 cc = 12 × (10–2m)3 = 12 × 10–6 m3 = 1.2 × 10–5m3 1 millenium = 1000 years = 100 × 10 years = 100 decades. There are 11 squars darkened.  Total area = 11 × Area of 1 square = 11 × 1 cm2 = 11 cm2 On 12 hour clock, five = 3h – 45 min PM Time on 24 hour clock = (12 + 3)h 45 min = 15h. 45min. 1 millenium = 1000 years = 1000 × 365 days

 1day 6.

7.

8.

9.

10.

11.

1 millenium 365  1000

1 decade = _______ minutes 1 decade = 10 years = 10 × 365 × 24 × 60 min = 5256000 min = 5.256 ×106 min. 1 year = ________ seconds 1 year = 365 days. = 365 × 24 × 60 × 60 s = 365 × 86400 s = 31.536000 s = 31.53×106 s V = 5ml = 5cc (or) 5 cm3

12.

= 5×(10–2 m)3 = 5×10–6 m3. V = 10,000 litre = 104 × 103 ml. = 107 cc = 107 × (10–3 m)3 = 107 × 10–6 m3 = 10m3 V1 = 26 ml V2 = 6cm3 = 6 cc = 6ml Vnew = 26 + 6 = 32 ml Me = 9.11 ×10–31 kg. 1 kg = ______ electrons. Let ‘n’ be the no. of electrons.  n × me = total mass



n

Total 1kg  me 9.1 1031 kg



n

10 1030 9.1

= 1.097×1030 = 1.1 ×1030 m1 = 0.32 kg = 300 g = 3×102 g m2 = 0.32 mg = 0.3 ×10–3 g = 3×10–4 g m3 = 0.3 ×10–6 g = 3×10–7 m4 = 3000 g = 3×103g.  3×103g > 3× 102g > 3×10–4 g > 3×10–7g m4 > m1 > m2 > m3

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6th Class Physics

100

IIT JEE WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

11

12

Ans

C

B

B

C

A

B

D

B

D

D

A, B, C

A, B, C

Q.no

13

14

15

16

17

18

19

20

21

22

23

Ans

A, C, D

A, C, D

B

A

C

B

A

9

1

7

6

Q.no

24

Ans

Aq; Br; Cs; Dp

25 (i) (c) ; (ii)  (d) (iii) (a) ; (iv)  (b)

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1. Chand’s height is 10 cm more than the 1 m mark on the meter scale. Hence, his height is equal to 110 centimetres, i.e., 1 m and 10 cm. 2. It can be observed from the given figure that the lengths of pencils I and II are 4.5 cm and 3 cm respectively. 3. The relative change in the position of the ants is the change in the distance between them. Initially, the distance between the ants is (2 cm – 1 cm =) 1 cm. After sometime, one ant is at the 10 cm mark and the other is at the 7 cm mark on the ruler. Hence, the distance between them is (10 cm – 7 cm =) 3 cm. Hence, the relative change in the position of the ants is (3 cm – 1 cm =) 2 cm. 4. A measuring tape is a long strip of plastic, rubber, or cloth that has markings on it to measure length. Hence, a measuring tape can be used to find the tallest student in a group of four. 5. A measuring tape is a long strip of plastic, rubber, or cloth that has markings on it to measure length. Hence, Sandeep can use a measuring tape to measure the height of his study table. 6. Peter runs 10 m in one second i.e., he can cover 1 m in

1 s. 10

Hence, he can run 200 m in

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1  200  20s 10

7.

8.

1 cm = 10 mm   2.4 cm = 2.4 × 1 cm = 2.4 × 10 mm = 24 mm II. 1 km = 1000 m And, 1 m = 1000 mm  1 km = 1000 × 1 m = 1000 × 1000 mm = 106 mm  1 mm = 10–6 km  3.1 mm = 3.1 × 1 mm = 3.1 × 10–6 km Length of the thread = 10-hand spans The thread is wound around the cylinder 5 times. Hence, the length of one wind of the thread I.

around the cylinder

9.

2-hand spans

The circumference of the given cylinder is nothing but the length of the thread that is wound around it. Hence, the circumference of the cylinder is two-hand spans. Initial length of the ice pole = 120 cm After every half hour, its height reduces to half. The given table illustrates the height of the pole after a period of half hour (in centimeters). Time Height 1 120 After hour  60 cm 2 2 60 After 1 hour  30 cm 2 1 30 After 1 hour  15 cm 2 2 15  7.5 After 2 hours 2 Hence, after two hours, the height of the pole will be 7.5 cm. Since 1 cm = 10 mm, the height of the pole after 2 hours will be 7.5 × 10 = 75 mm.

Measurement Solutions

10.

101

The length of the table is 8 times the length of the given thread. Akram has folded the thread twice at its mid point. Thus, its length is reduced to one-fourth of the original length (as shown in the given figure).

Circumference 23.

Original thread Length  one half First fold

Length  one forth Second fold

1 th of 4 the original thread must be placed 8 × 4 = 32 times along the length of the table to measure its length. A, B, C A, B, C A, C, D A, C, D 1 deci metre = 10–2 m 1 milligram = 10–3 g 1 cm3 = 1×(10 mm)3 = 103 mm3 2 1 km = 1 × (103 m)2 = 106m2 1 millisecond = 10–3s LS = x LL = 2x Give LR = 18 x = 9 × 2x LR = 9(LL) =9 R = T + 5 cm _______ (1) M = R – cm _______ (2) M = 0.55 _______ (3) M = 55 cm. M = T + x = ? _______ (4) Substituting (3) in (2), we get R=m+4 = 55 + 4 = 59 cm.  T = R – 5 = 59 – 5 = 54 cm.  55 = 54 + x x = 1 cm.  Length of thread = 14 hs n=2

18. 19. 20.

21.

22.

LR = 240 cm. LW = 40 cm. LR = nLW L R 240  6 LW 40 (A) 1 hecta gram = 102 g (B) 1 deca gram = 101 g (C) 1 milligram = 10–3 g (D) 1 micro gram = 10–10g  A  q; B  r; C  s; D  p (i)  c (ii)  d (iii)  a (iv)  b n

24.

Hence, this folded thread with length

11. 12. 13. 14. 15. 16. 17.

14  7 hs 2

25.

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6th Class Physics

102

2. MOTION AND FORCE SOLUTIONS

FORMATIVE WORKSHEET KEY 1 C, D 11 B

2 D 12 C

3 B 13 A

4 A 14 C

5 A 15 A

6 A, B, C 16 C

7 D 17 C

8 C 18 D

9 D 19 A

10 C

CONCEPTIVE WORKSHEET KEY 11 D

12 C

13 C

14 D

15 C

16 D

17 C

18 B

19 C

20 D

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

Vibratory Motion. Because strings does not move as a whole.

SUM MATIVE WORKSHEET

2.

KEY 1 B 7 A 13 A Linear and rotational. As ball rolling down it covers some distance along with the rotation.

3.

In oscillatory motion body moves to-and-fro or back-and-forth at regular intervals of time. Hence all oscillatory motions are periodic in nature.

4.

Motion, Rest

5.

Movement of a toy car around a circular road.

Rest

7.

Motion

8.

Yes. Motion of wheels of a moving car.

9.

Periodic

10. Periodic Motion

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3 B 9 D

4 B 10 C

5 C 11 C

6 D 12 A

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

It covers a distance of circumference of circle during its circular motion. 6.

2 C 8 C

2.

The relative change in the position of the ants is the change in the distance between them. Initially, the distance between the ants is (2 cm “ 1 cm =) 1 cm. After sometime, one ant is at the 10 cm mark and the other is at the 7 cm mark on the ruler. Hence, the distance between them is (10 cm “ 7 cm =) 3 cm. Hence, the relative change in the position of the ants is (3 cm “ 1 cm =) 2 cm.The correct answer is B. When a stone is dropped in still water, it produces waves on the surface of water. In the given situation, the cork starts moving up and down because of the waves on the surface of water, i.e., the cork starts moving in a periodic motion as a result of the wave motion produced on the surface of water.The correct answer is C.

Motion & Force Solutions 3.

4.

5.

6.

7. 8. 9.

The stone is moving along a circular path around the vertical rod. Hence, the stone is moving in a circular motion.The correct answer is B. The tires of a bicycle or any other automobile rotate along a circle or in a circular path. Hence, the motion of the tires of a bicycle is circular. The bicycle moves forward in a straight line. Therefore, the bicycle’s motion is linear. The correct answer is B. The motion of the girl on the swing repeats itself after a particular period of time. Hence, the girl has a periodic motion on the swing. The correct answer is C. A body is said to possess rotational motion if it rotates about a fixed axis. Since a top rotates about its own vertical axis, it possesses rotational motion.A body is said to possess periodic motion if it repeats its motion after a fixed interval of time. Since the bob of a pendulum exhibits such motion, it possesses periodic motion.The correct answer is D. In order to push or pull an object, a force must be applied. Roger noticed a book lying on a table . In order to move the book, he must apply a force. Here, we need to investigate the relation between

103 11. Here, the student is required to determine the change in the amount of force required when the box moves over wheels. Since frictional force opposes the motion of the box, the boys have to apply a large amount of force. If wheels were present below the box, then the frictional force between the box and the surface would decrease. As a result, the boys would have to apply lesser force to move the box. The correct answer is C. 12.

The total force on the rope toward the right is 60 N, i.e., applied by Mark. The total force on the rope toward the left is 40 N + 20 N = 60 N, i.e., applied by Sandy and George. Hence, the net force on the rope is 60 N – 60 N = 0 N. The correct answer is A.

13. The total force applied by the four boys is the sum

the direction of force and the motion of the

total of the respective forces applied by them, i.e., As a result of the presence of sand on the ground, the frictional force between the box and the ground is 15 N. The total force experienced by the box is

wheelchair. The direction of force on the wheel

25 N + 25 N + 30 N + 35 N = 115 N toward the

chair will be along its direction of motion. Initially

left. Frictional force opposes the motion of a moving

the wheel chair is pushed from West to East. It

object. As a result, the frictional force experienced

then takes two left turns, i.e., the direction of motion

by the box is 15 N toward the right. Hence, the

of the wheelchair becomes reverse, (from East to

total force experienced by box is the difference

West). Finally, the chair takes a right turn before

between the total force applied by the boys and

coming to a halt, i.e., the direction of motion of the

the frictional force, i.e., 115 N “ 15 N = 100 N

wheelchair is from South to North. Hence, before

toward the left. The correct answer is A.

the wheelchair comes to a halt, the direction of

HOTS WORKSHEET

force on it is from South to North. The correct

KEY

answer is D. 10. Here, the student is required to investigate the relationship between the direction of applied force and the motion of the car. Since the car moves toward East, the applied force that stops the car must be in the opposite direction. Hence, the

1 A 6 A 11 D

2 C 7 A 12 A

3 A 8 C 13 A

4 B 9 B 14 C

5 C 10 D 15 C

direction of the applied force is toward West. The correct answer is C. www.betoppers.com

6th Class Physics

104

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

2.

3.

4.

5.

6.

The pedal of a bicycle moves in such a way that its distance from a fixed point (axle) remains the same. Hence, the bicycle pedal has only circular motion. The wheel of a bicycle moves in such a way that the distance of any point on the wheel from the centre remains the same during its motion. Also, all points on the wheel move laterally along a straight line when the cycle moves. Hence, the bicycle wheel has both circular and linear motion. Hence, the pedal of a bicycle has only one type of motion, while its wheels have two types of motions.The correct answer is A. An object is said to possess circular motion if its distance from a fixed point remains constant during its motion. The distance of all the points on fan blades from the centre of the fan remains the same during the motion of the blades. Therefore, the blades of a fan have circular motion. T h e correct answer is C. When a leaf falls from a height, it falls along a straight line. Thus, a falling leaf traces a straight path during its motion. Therefore, it only has rectilinear motion. Hence, a falling leaf has only one type of motion. The correct answer is A. An object is said to have circular motion if its distance from a fixed point remains constant during the motion. For example, the motion of the hands of a clock exhibit circular motion. An object is said to possess periodic motion if it moves back and forth repeatedly about a fixed point. For example, the motion of the bob of a pendulum exhibits periodic motion. The correct answer is B. An object is said to have rectilinear motion if it moves along a straight path. When a soldier marches, he is moving in straight path. Hence, the motion of a marching soldier is an example of rectilinear motion. The correct answer is C. The contact between the flag and the wind causes

Joanna is using her fingers to hit the striker and the coins. This implies that she uses muscular force for pocketing the queen.The correct answer is C.

9.

The magnets exert magnetic force which causes them to stick to the refrigerator, as the latter contains iron in it.

10. All objects having mass attract each other by a force known as gravitational force. Therefore, the two magnets attract each other by gravitational force.Two magnets can attract or repel each other by magnetic force. Like poles of two magnets attract each other, while their unlike poles repel each other. The magnets repel each other as their like poles face each other in the given figure.

Since the inclined plane is rough, the small bar magnet experiences frictional force in the opposite direction, as shown in the following figure.Hence, the small bar magnet experiences gravitational, magnetic, and frictional forces.The correct answer

force between the object and Earth or any other

is D. 11. This question is successfully answered by the student who can recognize the various forces that act on the magnets. All objects having mass attract each other by a force known as the gravitational force. Since both magnets have mass, they attract each other by gravitational force. Like poles of a magnet repel each other, while unlike poles attract each other by a magnetic force. Since the magnets are placed on a frictionless surface, they do not experience any frictional force.Hence, the magnets will experience magnetic and gravitational forces. The correct answer is D. 12. The force of gravity, which is exerted by Earth,

planet. Hence, when a wooden box is suspended

attracts objects toward itself.Hence, a ball that is

by a spring balance, the spring stretches because

thrown up returns to the surface of Earth because

Earth’s gravitational force pulls the box.The correct

of gravity.The correct answer is A.

the flag to flutter. Hence, the flag flutters because of the application of a direct force. 7.

8.

Weight of an object is the measure of gravitational

answer is A. www.betoppers.com

Motion & Force Solutions

105

between the force on the ball and its direction of

2.

A ball falls on the ground because of the

motion. When the ball moves upward, the force

gravitational pull of Earth. There is no contact

exerted on the same is in the downward direction.

between the ball and Earth. Hence, this process

This force, caused by Earth’s mass and that of the

is caused by indirect application of force.The

ball, is known as the force of gravity. This force

correct answer is A.

tends to slow the ball down and eventually make it

3.

When two magnets are brought near each other,

come back to Earth’s surface. Hence, the direction

they attract or repel each other depending on their

of force on an upward moving ball is from up to

polarity. The movement is caused by magnetic

down. The correct answer is A.

force between them which is an indirect force as

14. Knowledge of the relation between motion and

magnets are not in contact. The correct answer

force is required to answer this question correctly.Earth revolves around Sun in 365 days.

is D. 4.

The magnet placed at the bottom of the ride repels

This motion is caused by the gravitational force

the magnet that is fitted below the capsule, as both

that acts between Earth and Sun.The correct

have the same poles facing each other. This causes

answer is C.

the ride to slow down as it reaches the surface

15. Gravity is a universally attractive force. It cannot

because magnetic repulsions increase as the

repel a body. Magnetic force can attract as well

distance between the base of the ride and the

as repel a body. Two magnets can push or pull

capsule decreases.The correct answer is B.

each other, depending on their polarity, whereas,

5.

Trenton uses his arms to rotate the lever which

two bodies having mass can only attract each other.

draws the bucket out of the well. Hence, he uses

Hence, the given statement is correctly completed

his muscular power to pull the bucket.The correct

by row C. The correct answer is C.

answer is C.

IITJEE WORKSHEET 1 2 B A 6 7 C D 11 12 ABC ABD 16 17 B D

KEY 3 D 8 B 13 ABCD 18 A

4 5 B C 9 10 D B 14 15 BD ACD 19 B

16.

As the body comes to its initial position of start, its displacement is zero and distance is equal to circumference of the circle.

17.

As the body comes to its initial position of start, its displacement is zero.

18.

The distance travelled is equal to the total path covered by the body and is equal to 4 km.

19.

Distance = AB + BC + CD = 4 + 3 + 2 = 9 km.

20.

A– t; B – r ; C – q ; D – p

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1. To lift the load, William is using his hand to pull the rope of the pulley system. The pulley system rotates the wheel, as a result the lift the load. Hence, William is using his muscular force to life the load.The correct answer is B. www.betoppers.com

6th Class Physics

106

3. ENERGY AND WORK SOLUTIONS

FORMATIVE WORKSHEET KEY 1 B 11 C 21 D 31 D

2 A 12 B 22 B 32 C

3 D 13 C 23 B

4 C 14 C 24 D

5 B 15 A 25 C

6 A 16 D 26 A

7 C 17 D 27 B

8 A 18 B 28 D

9 A 19 D 29 C

10 B 20 D 30 D

9.

(i) F = 5 N, S = 2m W=F×S = 5 × 2 = 10 Nm = 10 J (ii) m = 2kg, h = 2m, g = 9.8 m/s2 W = mgh = 2 × 9.8 × 2 = 39.2 Nm = 39.2 J 10. m = 15 kg, h = 2.0 m g = 9.8 m/s2, W=? W = mgh = 15 × 9.8 × 2.0 = 294 J 11. W = 4900 J, m = 50 kg g = 9.8 m/s2, h=? we know that, W = mgh

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

2. 3.

4.

5.

Force (F) = 25 N Displacement (S) = 10 m Work done (W) = F × S = 25 N × 10 m = 250 J. 2.35 × 105 J F = 1023 N S = 34 m W = F× S = 1023 × 24 = 34782 J F = 27.5 N S = 12.3 m W = F× S = 27.5 × 12.3 = 338.25 J W = 55, 000J S = 25 m F=?

W 55000   2200 N S 25 m = 50 kg, h = 72 m, g = 9.8 m/s2 W = F × S = mg × h = 50 × 9.8 × 72 J W = F×S  F 

6.

 50  7.

W = 2500 J, g = 10 m/s2 we know

m 8.

98  72 J = 35280 J 10 h = 5 m, m= ? W = mgh

W 2500  kg = 50 kg gh 10  5

m = 100 kg, h = 10 m, W = ? work done against gravity W = mgh = 100 × 9.8 × 10 J = 9800 J

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h 12.

13.

W 4900 4900   m  10 m mg 50  9.8 490

m = 2 kg, v = 0.1 m/s 1 2 Now K.E = mv 2 1 2 =  2   0.1 = 0.01 J 2 Let two bodies be A and B A B m1 = m2 = m v1 = v v2 = 3v 1 1 2 2 K.E1 = mv K.E2 = m  3v  2 2 1  9 mv2 2 1 2 mv K.E1  2 Now K.E 2 9 1 mv 2 2 K.E : K.E = 1:9  1 2 Thus, the ratio of the kinetic energies is 1 : 9. or 1  We know, K.E.  mv 2  K.E  v 2 m is cons tan t  2



K.E1 v12  v  1  2  1: 9 2 K.E 2 v 2  3v  9

Energy and Work Solutions 14.

107

K.E = 1 J,

m = 1 kg, 1 2 We know that, K.E = mv 2 1 2 1 = 1 v 2  v2 = 2  v = 2 v = 1.4 m/s P.E = 1 J, m = 1 kg, g =10 m/s2, h=? we know that P.E = mgh P.E 1  J = 0.1 m h= mg 1  10

15.

v=?

12.

1 mv 2 2 1 1 1 2 2 2 = m  2v  = m  4v = 4  mv 2 2 2 = 4 × K.E

K.E =

14.

1 mv 2 2 1 1 1 2 2 2 = m  4v  = m  16v = 16 mv 2 2 2 = 16 × K.E A flying aeroplane has both kinetic and potential energy.

KEY 2 C 12 D 22 C 32 B

3 A 13 C 23 D 33 A

4 B 14 C 24 A 34 C

5 D 15 B 25 A 35 D

6 B 16 B 26 B 36 D

7 C 17 C 27 C

8 C 18 C 28 D

9 C 19 A 29 C

10 B 20 D 30 D

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 5. 6.

7.

Zero, as there is no displacement of the man. F = 567 N S = 20 m W = F× S = 567 × 20 = 11340 J W = 567.6 J S = 30.5 m W = F×S  F 

8. 9.

If the velocity an object increases 4 times, its kinetic energy increases 16 times K.E =

CONCEPTIVE WORKSHEET 1 B 11 A 21 C 31 D

When the velocity of a moving object is doubled, its kinetic energy increases four times.

W 567.6   18.6 N S 30.5

15.

If a spring is compressed. The potential energy of the spring increases.

16.

mass = 1 kg, g = 9.8 m/s2  W = mgh

= 1 × 9.8 × 1 J = 9.8 J 17.

18.

11.

Strong wind can turn the blades of a wind mill because it possesses kinetic energy.

h = 2m,

98  2 J  98 J 10

m = 1 kg, g = 9.8 m/s

h=5m 2

W = mgh = 1 × 9.8 × 5 J = 49 J 19.

m = 100 kg, g = 9.8 m/s2

h = 5 m,

 W = mgh

= 100 × 9.8 × 5 J

The kinetic energy of a body depends on its mass as well as on its velocity. Water stored at a height in a dam possesses only potential energy.

mass = 5 kg, g = 9.8 m/s2  W = mgh = 5 × 9.8 × 2 J = 5

When a body rolls down an inclined plane, it has both kinetic and potential energy.

10.

h = 1 m,

= 4900 J 20.

m = 1kg,

g = 10 m/s2, h = 5 m

 P.E = mgh

= 1 × 10 × 5 J = 50 J

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6th Class Physics

108

SUM MATIVE WORKSHEET HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

22. 23.

24. 25. 26.

27. 28. 29. 30. 31.

Work Motion Force 1m Position Motion Mechanical energy Electrical Heat and light Light Work done is zero as the displacement is zero. Work done by a body is the product of force and displacement. In electric bulbs, tube lights, etc., the electric energy first changes into heat energy and then light energy. When we speak in front of a microphone, the sound energy changes into electric energy During photosynthesis light energy changes into chemical energy. In charging a car battery, the electric energy changes into chemical energy. A wound up spring of a watch possesses potential energy. Nuclear energy is released in the form of heat and light energy. When a stone is projected vertically upwards its potential energy changes into kinetic energy. Kinetic energy = ½ mv2 . Therefore, increase in mass increases the kinetic energy. False. Magnetic energy is both attractive and repulsive. Only gravitational force is always attractive in nature. True False. When the string of a bow is stretched, the muscular energy is stored in the string and bow in the form of potential energy. It is this potential energy which makes the arrow shoot forward. True True False. In electric bulbs, tube lights, etc., the electric energy first changes into heat energy and then light energy. False. Nuclear energy. True True True C 32. C 33. B 34. A 35. D

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36. C 37. B 38. B 39. A 40. D 41. Speeding train. All others are examples of having potential energy. Speeding train is an example for a body possessing kinetic energy. 42. A stone lying on the top of roof. All others are examples of having kinetic energy. A stone lying on the top of roof is an example for a body possessing potential energy. 43. Solar cell. In coal, petrol, kerosene, etc., the chemical energy is basically the trapped solar energy. Solar energy is directly used in solar cells which are used in watches; calculators and artificial satellites.

HOTS WORKSHEET KEY 1 A 11 D 21 D

2 C 12 B 22 B

3 D 13 C 23 A

4 C 14 D 24 D

5 C 15 D 25 D

6 B 16 C

7 C 17 C

8 B 18 D

9 C 19 A

10 C 20 D

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1. 2.

3.

4.

5.

6.

Displacement is a vector quantity. It has both magnitude and direction. When brake is applied on moving car, its motion is retarded. It means that force by brake must be applied in the opposite direction of the displacement of the car.Therefore, the work done by the brake on the car is said to be negative. When displacement is in opposite direction to the force, then the work done is said to be negative and it is non-zero. In uniform circular motion, work done by perpendicular force on the particle is zero and speed of the particle is constant. So, kinetic energy of the particle is constant. Gravitaional force acting on the load, F =  mg = 10×9.8=98 N Net displacement of the load = AB = 4 m 4" Work done = F×s=98×4=392 J The correct option is C. Scientifically, work is done only when a force is applied on a body and it causes some displacement of the body along the line of direction of the applied force. Therefore, the directions of the applied force and the displacement of the body can be opposite. Criterion III suggests  that  the  direction  of  the

Energy and Work Solutions

109

applied force and that of the displacement must Change in K.E. of remain the same. However, this is not an essential 1 2 2 criterion for something to qualify scientifically as car II,  KII   2m   0    v   2 work done. 7. The work done in lifting a stone against the force  m  2v 2  of gravity is stored as the potential energy of the = (ii) 2 stone i.e., work done = potential energy of the body. 8. The ability of a body to do some work is known as 1  m  4v 2  energy. EK I 2  2  9. Work done in lifting the stone against the force of EK II  1 m 2v 2 1  E KI : E KII  2 :1   gravity is stored as the potential energy of the 2 stone.  13. Change in kinetic energy of the car is given by the 4" Work done = Potential energy of the body relation: 10. Energy of a body is defined as the ability to do some work by the body. 1 E K  m  v2  u 2  11. The work-energy theorem states that the change 2 in the kinetic energy of a body is the w o r k Where, done by the net force on the body. According to m = Mass of the car = 1200 kg this theorem, it can be written v = Final velocity of the car = 18 m/s Kfinal –K initial =W net u = Initial velocity of the car = 0 The correct answer is D. 12. B = 600 × 324 Change in kinetic energy of a body is given by the relation: = 194400 J Hence, the work done on the car is 194400 J. 1 E k  m  v2  u 2  14. The work-energy theorem states that the change 2 in the kinetic energy of a body is the w o r k Where, done by the net force on the body. According to m = Mass of the body this theorem, it can be written v = Final velocity of the body K final  K initial  Wnet u = Initial velocity of the body The correct answer is D. 15. Like poles of a magnet repel each other while unlike poles attract each other. For car I: For car II: In the given case, it is given that the two magnets do not come in contact with each other. This shows Mass = m Mass = 2m that the same poles, i.e. North poles of both the magnets, are close to each other. Therefore, the Initial velocity = 2v Initial velocity = v two magnets repel away from each other. The correct answer is D. Final velocity = 0 Final velocity = 0  16. Hydro power plants use the potential energy of water accumulated at a height to spin a turbine. (Since both the cars come to rest) So, we can say that mechanical energy is converted into electrical energy in hydro power plant. Change in K.E. of 17. Plastic is a non-biodegradable material. So, it cannot 1 2 2 be used as biomass fuel. car I,  E kI  m  0    2v   2 18. The main reason for the production of ocean waves is the winds that blow across the sea. 2 m  4v  19. Hydro power plants use potential energy of water  ____(i) 2 accumulated at a height to spin a turbine.

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6th Class Physics

110 20. In a hydropower plant, a large amount of water is stored at a height by means of constructing a high dam. Water at a height has large potential energy by virtue of its position. This potential energy of water is converted into kinetic energy as it falls. The kinetic energy of falling water is used to rotate the motor of the turbine in order to g e n e r a t e electricity. 21. Ocean thermal power plants are used to convert ocean thermal energy into electricity. These are established near coastal areas along the sea shore. These plants harness the energy that is present in the ocean by virtue of the temperature difference between the shallow and deep waters.The correct answer is D. 22. Kinetic energy possessed by strong winds blowing over the sea result in strong waves along the coastline. The energy possessed by the high rising waves is called as wave energy. 23. Solar cell is a device that runs on solar energy. It is an electricity producing device that converts solar energy into electrical energy. 24. In order to harness wind energy using wind mills, the speed of the wind must be at least 10 miles/ h. Therefore, wind power plants should be built only in regions with constant high wind speeds. 25. Some of the products that are used in the preparation of biogas are dung, residue of plants, crops, vegetable wastes, etc. These can replenish itself in nature. Therefore,biogas is a non-conventional sour ce of energy. Hence, statement I is  incorrect. Biogas is for med in a biogas plant by the decomposition of the wastes of livestock, in t he absence of oxygen. Hence, statement II is correct. Biogas contains about 75% methane. The gas thus produced by the decomposition can be stored in tanks. From these storage tanks, this gas is transported through pipes. Therefore, statement III iscorrect.The correct answer is D.

IITJEE WORKSHEET

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

2 3 4 5 6 7 8 9 10 C A D A A A D C C 12 D

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W 1762.2   3.6 m F 489.5 m = 125.7 g = 0.1257 kg g = 9.8 m/s2 W = 5.023 J S=? W = F× S = mg×s F = 137 N W = 223 J S=? W = F×S Zero, as there is no displacement of the dog. m = 100 g = 0.1 kg K.E = 20 J, v = ? 1 2 From definition, K.E = mv 2 1 2 20 =  0.1  v 2 v2   20  v2 = 20 × 20 20  v = 400 = 20 m/s v = 5 m/s, m = ? K.E = 25 J 1 2 Now K.E = mv 2 1  25   m  52  m  2 kg 2 When the velocity triples 1 1 2 2 K.E = mv =  2  15  = 225 J 2 2 m = 40 kg, v = 54 km/h = 15 m/s 1 1 2 mv2   40  15  = 4500 J  K.E = 2 2 m = 0.5 kg, P.E = 1.0 J, h = ? P.E = mgh P.E 1 h   0.2 m mg 0.5  10

W = F×S  S  2.

3.

4. 5.

6.

7.

8.

KEY 1 A 11 B

F = 489.5 N W = 1762.2 J S=?

13. 15. 17. 19. 21.

ABC ABD ABC ABC BC

14. 16. 18. 20. 22.

ABC AB BC ABD ABC

Energy and Work Solutions 23.

24.

F = 50 N

 P2  8 K.E

S = 10 m

Dividing (1) by (2) we have

W = F× S = 50 × 10 = 500 J W = 6000 J S = 25 m F=?

P1  P2

26. 27. 28.

C C B

29.

[A]

8 K.E

P1 : P2 = 1 : 2 32.

[A] m1 = 1 kg,

P12 K.E1 2m m   21  2  2 : 1 P2 K.E 2 m1 2m 2

33.

30.

P=?

K.E2 = 2K.E1

 P22  P12 

2mE

1  20 = 10

m2 = 4 kg

P1 = P 2

P12 KE1 2m m 4   2 1  2   4 :1 P2 KE 2 m1 1  P1  P2  2m2

31.

[D] Let two bodies A and B A

34. 35. 36. 37. 38.

abcd/srqp abcd/qspr abcd/rpsq abcd/rpsq F = 4N S=2m W = F×S = 4 ×2 = 8 J 38. m = 100 kg g = 9.8 m/s2 PE = 4900J h=?

B

m1 = 1 kg

m2 = 4 kg K.E1 = K.E2

P1 : P 2 = ?

 P1  2 K.E

PE = mgh or h 

PE 4900   5m mg 100  9.8

1 mv 2 2 1 1 2  2m   2v  = 8  mv 2 =8K.E1 K.E2 = 2 2

40. K.E1 =

P1  2 m1 K.E1

 P2 

K.E 2 2K.E1  P12  K.E1 K.E1

 P2  2 P1

4 = 2 kg m/s

[A] m1 = 1 kg,

 P2 

[D]

we know that

2

 P1

K.E1 P12 = K.E 2 P22

1 kg 10 K.E = E = 20 J,

=

m2 = 2 kg P1 = P 2

W 3200   4m F 800

m = 100 g =

P=

P12 2 K.E  P 2  8 K.E 2

 P1  1    4  P2 

F = 800 N W = 3200 J S=? W = F×S  S 

2 K.E

------------ (2)

2

W 6000   240 N S 25

W = F×S  F  25.

111

------------ (1)

2 m 2 K.E 2

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6th Class Physics

112

4. LIGHT WORKSHEET SOLUTIONS

FORMATIVE WORKSHEET

Angle of reflection , r = i =

KEY 1 2 B * 16 18 B A 25 26 B C

3 4 5 6 ABC C C A 19 20 21 22 B A B A 27 B

We know that, glancing angle, g = 90 - i

7 8 D ABCD 23 24 B B

 g  90  12.

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

An optical medium which has a uniform composition throughout is called homogeneous medium. Examples: Vaccum, diamond, distilled water, pure alcohol, etc. The bodies which do not allow the light energy to pass through them are called opaque bodies. Examples: Bricks, wood, metals, etc. 2. A – 1, 2, 3, 4 ; B – 2, 5; C – 1, 3; D – 4, 5 3. Opaque objects do not allow the light to pass through them. 4. Light can travel through vaccum also and needs no medium to propogate. 5. When the rays of light originating from a point ,travel 13. in various directions, then the collection of such rays is called divergent beam. 6. When the rays of light travels parallel to each other,then the collection of such rays is called parallel beam. 7. When the rays of light coming from different directions, meet at a point then the collection of such rays is called convergent beam. 8. All the given statements are correct. 9. Normal incidence  Angle of incidence = 00 ; Angle of deviation, d = ? We know that, d = 180 - 2i = 180 - 0 = 1800 10. We know that, d = 180 - 2i or d = 180 - ( i + r ) [  i = r]  d + i + r = 1800. Therefore, the sum of angle of incidence , angle of reflection and angle of deviation is equal to 1800. 11. Angle of deviation = d; i = ? ; r = ? ; g = ? We know that, d = 180 - 2i  2i - 180 - d or i =

180  d 2 www.betoppers.com

180  d 2

180  d d  2 2

Let the initial angle of incidence be x. M1 and M2 are the initial and final positions of the mirror. N1 and N2 are the initial and final positions of the normals. AO is the incident ray , OB is reflected ray before rotation and OC is the reflected ray after rotation. We need to find the angle through which the reflected ray rotates i.e., BOC . By solving, we get BOC = 2  . N1

A

N2

B

x+ x

 y

x

x



=

+



C

?

M1 O M2

The angle between the incident ray and reflected ray = x  i = r = x/2 (i) After the mirror is rotated through an angle of x/2 in clock wise rotation, then the new angle of incidence becomes 3x/2 and the new angle of reflection becomes 3x/2. Therefore the angle between the incident ray and reflected ray = New angle of incidence + New angle of reflection = 3x /2 + 3x/2 = 3x. (ii) After the mirror is rotated through an angle of x/2 in anti clock wise rotation, then the new angle of incidence becomes x/2 and the new angle of reflection becomes x/2. Therefore the angle between the incident ray and reflected ray = New angle of incidence + New angle of reflection = x /2 + x/2 = x.

Light Solutions

113

14.



15.

Angle of incidence = 150, Angle of reflection = 150 ; The reflected ray makes an angle of 300 with the vertical and 600 with the horizontal. ( see the figure for further understanding) N2

N1

B C

i+





CONCEPTIVE WORKSHEET KEY 1 2 3 4 5 6 7 A B ABCD A C B C 8 9 10 11 12 13 14 D A A A ABCD A B 15 16 17 18 19 20 21 D B C B A A A 22 23 24 25 B BD AC A

A

i+

i 2



i

 

HINTS/ ANSWERS TO THE SELECTED QUESTIONS

O

1. 2. 16.

Both the statements are correct, but statement-II is not the correct explanation of Statement - I.

17.

A – 1; B – 3; C – 2; D – 4

18.

When the rays of light, diverging from a point, after reflection or refraction, appear to diverge from another point, then the image so formed is called virtual image.

19.

20. 21. 22. 23. 24. 25. 26. 27.

3. 4. 5. 6. 7.

When the rays of light, diverging from an object 8. point, after reflection or refraction actually converge at some other point then that point is real 9. image of that object. 10. a-k, b-i 11. When the sun, the earth and the moon come to lie in a straight line, it causes eclipses. 12. A solar eclipse can occur only on a new moon day. 13. Shadows are formed when light falls on an opaque object. 14. The completely dark portion of a shadow is called 15. umbra. 16. A solar eclipse is caused when the moon comes between the sun and the earth. 17. When the moon is in the penumbra of the shadow of the earth, then partial lunar eclipse is formed. 18. A shadow which is partially illuminated is called 19. penumbra . 20.

Light travels in straight line and this is called rectilinear propogation of light. Sun emits light on its own and hence it is a luminous body. All the given statements are correct. A source of light which is of the size of the pin head is called point source. Light causes the sensation of vision. A point source produces a divergent beam. Bodies which do not allow the light energy to pass through them are called opaquen bodies. A plane mirror forms a virtual, erect and same sized image. Reflection takes place on a plane mirror. The part of light which is returned back into the same medium is called reflected light. Motion and still pictures projected in a cinema hall are real images. All the given statements are correct. Its virtual and erect image. Hence, it cannot be caught on the screen. The reflected ray rotates by 20°. Statement - I is false, Statement - II is true. Both Statements are true, Statement - II is not correct explanation of Statement - I. When a mirror is rotated through an angle  the reflected ray from it, turns through an angle of 2 . i + r = 90  i = r = 45°. i = 60° D = 180 – 2i = 180 – 2 × 60 = 180 – 120 = 60° For a plane mirror, image distance = object distance. Therefore, the image is formed at a distance of 10 cm from the mirror.

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6th Class Physics

114

SUM MATIVE WORKSHEET KEY 1 2 C D 11 12 A B

1.

2.

3.

4.

5.

6.

7.

8.

3 4 5 6 7 D B D D B 13 14 15 16 17 C A A D B

8 C 18 C

9 10 A C 19 20 C C

The image formed by a pin-hole camera is shown in the given figure.

9.

It can be observed that the image of the candle is upside down. Also, the image is smaller in size relative to the object. Hence, the image formed by a pin-hole camera is inverted and diminished in size. Shadows are physical entities, which are real. These can only be obtained on screens. A screen may be a wall, a cardboard sheet, or even ground. Hence, statement II is  correct. Shadow is also defined as a region on a screen that is devoid of light. Its colour is black or grey. Hence, statement III is also correct. When light falls on a mirror, it gets reflected back by it. Thus, the path of light gets changed. Hence, a mirror changes the direction of incident light. Light travels in a straight line only. A straight line joining the flame of the candle to the prism cuts at point II on the cardboard sheet. Hence, Alam should make a hole at this cut point so that he can project a beam of candle light on the prism. Shadows are formed in a region devoid of light. When light coming from a source is obstructed by opaque objects (such as roses), then shadows are formed on a screen. Since shadows are regions that are devoid of light, shadows are always black in colour. Hence, shadows of both roses will be black. Essential objects required to form a shadow are a light source and an opaque object. Thus, a shadow of a book can be formed on the screen when light coming from the bulb is obstructed by the book. Hence, objects like bulb, book, and screen can be used to form a shadow. Transparent objects allow light to pass through them completely. Every thing is clearly visible through these objects. A sheet of carbon is opaque. It does not allow light to pass through it. Hence, visibility through it will be

10.

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11.

12.

13.

14.

15.

16.

17.

zero. Nothing can be seen through a carbon sheet. Glass sheet is a transparent object. It allows light to pass through it completely. Hence, visibility through it will be clear. Any object can be easily seen through a glass sheet. Tracing paper is a translucent object. It allows light to pass through it partially. Therefore, visibility through it is not clear. Objects cannot be seen clearly through a tracing paper. Objects that allow light to pass through them partially are known as translucent objects. Objects that allow light to pass through them completely are known as transparent objects. Object that do not allow light to pass through them at all are known as opaque objects. Butter paper is a translucent object. It allows light to pass through it partially. The message can be seen clearly only if it is viewed through a transparent material. Amit will be able to read the message most clearly through a thin glass. A translucent material allows only some light to pass through it. Objects look blurred when viewed through translucent materials. Among the given alternatives, a tracing paper can be used by Matthew as a sample of a translucent material. A shadow is formed when light is blocked by an object. As a result, light rays are not present in the shadows. Therefore, the color of the shadow of an opaque object is always black. It does not depend on the color of the opaque object or the color of the screen upon which the shadow is formed. Flame of a candle is not stationary (it slightly moves to and fro with air) the shadow of the pen also moves to and fro in accordance to the candle flame. This suggests that light travels in a straight line and cannot travel in a curved path. A clear shadow can be formed only by opaque objects. This is because they do not allow any light to pass through them. Hence, a clear shadow is obtained on a screen because it is formed by an opaque object. If one cannot see through an object at all, then it is classified as being opaque. Hence, one cannot see beyond the door of a closed room because it is an opaque object. The direction of a light ray changes as it passes from one medium to another. This phenomenon is called refraction of light. When a ray of light is incident on a transparent glass sheet, it refracts the light ray, as shown in the given figure.

Light Solutions

115

18. Transparent objects allow light to pass through them completely. One can see through these objects clearly. 19. An object that allows light to pass through it partially is called a translucent object. On looking through a translucent object, the object on the other side cannot be seen clearly. Therefore, one can identify a translucent object by viewing through it. Hence, Mushtaq must have viewed through the given 3. objects in order to identify the translucent object. 20. The base of a conical object is round or in the shape of a circle. When a beam of light falls from the top of a cone, a circular shadow is formed as represented in the given figure. Sunlight 4.

Conical object

5.

Hence, the statement made by student II is  also correct. The correct answer is C. Whatever be the orientation of the conical object in front of the sun, its shadow will not have a rectangular shape. This is because the object does not have a rectangular surface. Hence, its shadow will not be of a rectangular shape. The correct answer is C. The glass jar that contains the most opaque liquid will cast the darkest shadow. Hence, jar B, which contains coffee, will cast the darkest shadow. The correct answer is B. Object C will form the shadows shown above as

Circular shadow

HOTS WORKSHEET 1.

2.

Light travels in a straight line only. Light coming from a torch requires a straight path in order to reach the screen. It can be observed that only pipe II is straight. Thus, only through pipe II, light can reach the screen. Hence, only point N on the screen will light up. The correct answer is B. A funnel has a circular base. If light falls from the 6. top of a funnel kept vertically, then a circular shadow of the funnel would form (as shown in the figure below). 7.

8. Hence, the statement made by student I is correct. Also, the base and/or top of a bottle is circular. When light falls from the top of a bottle kept vertically, a circular shadow of the bottle would form (as shown in the figure below).

The correct answer is C. When an object is placed in front of a source of light, a shadow is formed. Hence, the ball will cast a shadow when it is placed in front of a flash light. The correct answer is C. Usually, Sun has either set or is at the horizon between 6:00 p.m. and 8:00 p.m. Hence, the faintest shadows can be observed between these hours. The correct answer is D. Shadows formed by objects are shortest at noon and longest in mornings and evenings. The shadow of the tree in the evening will be longer than its shadow at noon. Hence, the length of the shadow of the tree in the evening would be 4 m. The correct answer is D. www.betoppers.com

6th Class Physics

116 9.

10.

11. 13. 15. 17. 18.

When a ray of light gets reflected, the angle of incidence and the angle of reflection with the perpendicular to the plain are always equal. If the incident ray of light is perpendicular to the plain, then the reflected ray of light will also be perpendicular. The correct answer is C. The shadows formed by objects are shorter at noon and longer in mornings and evenings. The shadow of the pole in the evening will be longer than its shadow at noon. The correct answer is A. (B) 12. 40 cm 45 cm 14. (a) 60 m/s(b) 80 m/s(c) 40 m/s 0 60 16. 90 cm 0 50 The angle that the ray makes after each reflection is clearly labelled in the adjacent figure . It is clear that the final ray makes an angle of 600 with the horizontal, or in other words it emerges parallel to Mirror 1.

M2

600

The distance moved by the image II’ = MI’ – MI = 20 + x 20 – x = 40 cm

 Speed of image =

40  40 cm / s 1

IITJEE WORKSHEET 1 2 3 4 A D A A 8 9 10 11 C B B D 15 16 17 18 ABC ABC A C 22 23 50° 90°

5 A 12 ABCD 19 A

6 7 C C 13 14 ABC AB 20 21 B 40°

HINTS/ ANSWERS TO THE SELECTED QUESTIONS

0

30

17.

0

30

600 600

600

M1 19. The first image at M1 is formed at a distance of 4 cm behind it. The first image at M2 is 6 cm behind it. The second image at M 2 is at a distance of 4+10=14 cm behind. M2. Therefore, the distance between the first image at M 1 and second image at M 2 is 4+14+10=28 cm. 20. The speed of image =

Distance travelled by image Time Let us consider that the mirror has moved for 1 second.  The distance travelled by mirror = 20 cm/s Let the initial distance between object and mirror be x. From the figure, it is clear that OM = x  MI = x Let M’ be the final position of the mirror.  New object distance = OM’ =( x + 20) cm  New image distance = M’I’ = ( x + 20) cm www.betoppers.com

AO is the incident ray and OB is the reflected ray. Since the two rays are at right angles, the angle between incident ray and reflected ray is (AOB  90) . Given, the incident ray and the reflected ray are at right angles i.e. i + r = 90° Angle of incidence (i) = ? We know, angle of incidence (i) = angle of reflection (r) i + r = 90°  i  i  90  2i  90  i  45 As i and r are same, therefore, i = r = 45° each 18. Suppose OM1 is the horizontal plane mirror and OM2 the second mirror. Let the angle between the mirrors be 

Light Solutions According to the laws of reflection, ABM1  OBC1  45 Again, since CD and OM 1 are parallel, DCM 2   According to the laws of reflection, DCM 2  BCO   Now, in COB . OCB  CBO  COB  180 or  + 45° +  = 180° 1   = 67 2 19. Let PO and OQ be the two plane mirrors inclined at an angle  A light ray AB is incident on PO at B. BC is its reflected ray incident on OQ at C, such that CD is the final reflection. Given, AB||CD,  =?

117 Given, CRS  30  BRQ  30 (g i  g r ) 21. 22. 23.

24. 25. 26. 27. 28. 29.

In QBR,(90           10 Angle of incidence = 40°  Angle of reflection = 40° i + r = 100°  i = r = 50° Angle of incidence = 90 – 45 = 45 ° Angle between incident ray and reflected ray = i + r = 45 + 45 = 90° A - q, B - p, C - s, D - r A - q, B - r, C - s, D - p A - r, B - p, C - s, D - q A - q, B - p, t, C - s, D - r A - q, B - p, C - r, D - s A - s, B - p, C - q, D - r



Let x be the angle between BC and the mirror OQ. ACQ  x (Glancing Angles are equal) As AB and CD are parallel to each other, ABC  CDB  180 CDB 180  2 From the figure, x + x + (180 –2  ) = 180°. x In BOC,(90  )      180    90 Therefore, the angle between two mirrors is 90°. 20. AB and BC are two mirrors and the angle between them is 70°. Light ray travels along the path PQRS, such that RS is the reflected ray of second mirror.

The angle of incidence on first mirror be  . BQR  90   ( It is the glancing angle)

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6th Class Physics

118

5. ELECTRICITY SOLUTIONS 9.

FORMATIVE WORKSHEET KEY 4 D 11 C 18 B 25 AC

5 A 12 A 19 D 26 B

6 A 13 D 20 C 27 A

7 B 14 B 21 B

8 B 15 B 22 *

9 A 16 C 23 A

10 C 17 A 24 A

10.

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

2.

3.

4. 5.

6.

7.

8.

i = 10 mA = 10 ×10–3A t = 10 min = 10 × 60 sec. Q = it = 10 × 10–3 × 10 × 60 =6C Q = 100 C t = 4 sec Q 4 i  = 0.04 A t 100 t=? Q = 10 C i=2A Q = it = 10 × 2 = 20 C Electric current can pass through iron. Hence, Iron is a good conductor of electricity. The handle of an electrical repairing tool should be made of an electrical insulator. Tin is a good conductor of electricity, i.e., electric current can pass through it. Hence, tin cannot be used to cover the handles of electrical repairing tools. Wood is a bad conductor of electricity. The circuit will not become complete on inserting wood in the gap. Hence, the bulb will not light up. Insulators are those materials that do not conduct electricity. Plastics cannot conduct electricity. Hence, plastic cup is an insulator. In order to answer this question correctly, the student must be able to classify materials as electrical insulators and conductors. Electric wires are coated with plastic because plastic is a good electrical insulating material. This minimizes the unavoidable contact of the wire with other parts of the circuit or living tissues.

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11. 12.

13.

14.

15.

16.

In order to answer this question, the student must be able to identify whether a material is a good or bad conductor of electricity. To light up the bulb, points P and Q must be connected by an electrically conducting material. Iron is a good electrical conductor. Hence, the bulb will light up when points P and Q are connected with a plate made of iron. In order to answer this question, the student must be able to classify materials as electrical conductors and insulators. Copper is a good conductor of electricity. Therefore, when points P and Q are connected with a copper rod, a short circuit will occur in the battery and current will not pass through the bulb. Hence, the bulb will not light up. Plastic is an electrical insulator. Hence, plastic cannot be used to make electrical wires. Overhead electric lines transfer a high voltage of electricity and ceramics is an insulator of electricity. Therefore, ceramic pulleys are used to prevent electric wires from touching the poles. Graphite is an allotrope of carbon and is a good conductor of electricity. Hence, it cannot be used an electrical insulator. Wood is a very good electrical insulator. Therefore, the possibility of receiving an electric shock while working on an electric line is minimized by standing on a wooden plank. This simple problem can be solved by analyzing the given circuit. The complete circuit should consist of a bulb, a switch, and an energy source, such as a battery. The given circuit does not contain any battery or energy source. Hence, the bulb will not glow on closing the switch. The bulb will glow, when the constructed circuit is closed. Using the given four wires, bulb, switch, and battery, a closed circuit can be constructed as,

Electricity Solutions

119

17. By reversing the terminals of the battery in the given 8. circuit, the direction of the current flowing through the circuit will reverse. The functioning of the bulb does not depend on the direction of current flowing through it. Hence, there will be no effect on the operation of the bulb. The bulb will remain glowing as before. 9. 18. If bulb 1 gets fused, then the equivalent circuit can be represented asi.e., the circuit breaks. Since the circuit of bulb 2 becomes incomplete, it 10. will stop glowing. 11.

12. 22. a  2; b – 3; c  5; d – 1

CONCEPTIVE WORKSHEET KEY 1 2 B A 11 12

3 4 5 6 C D A A 13 14 15 16

C

D

A

D

B

A

7 8 9 10 A C A B 17 18 19 20 AB A D C CD

13.

14.

21 22 3v A

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 3.

4. 5.

6.

7.

On closing switch I, the given electrical circuit will not be complete. Hence, on closing switch I,the bulb will not glow. Electric current can pass through iron. Hence, Iron is a good conductor of electricity. The electrical circuit constructed by Robert will be complete when the positive terminal of the battery is connected to the point P. Hence, the bulb will glow when the positive terminal of the battery is connected to the point P. The circuit shown in alternative A will be complete when the switch is closed. As a result, the bulb will glow. However, the circuit will not be complete when the switch is open. As a result, the bulb will not glow. Therefore, the bulb can be operated by the switch in the circuit. Andrew should connect the bulb and the fan such that the voltage across the fan and the bulb is the same. Hence, Andrew should connect the bulb as shown in alternative A.

15.

16. 17. 18. 19.

Alex should add the switch in such a way that only bulbs N and P are controlled by it, i.e., the circuits of bulbs N and P should  be  incomplete when the switch is open and complete when the switch is closed. Hence, Alex should add the switch at point III. If a switch is placed at point I, then it will operate only bulb M. Bulb N will not be affected by the switch. The simple circuit containing all the components and the fan between the two bulbs is shown in the circuit diagram given in alternative B. The simple circuit containing all the components and the switch between the two bulbs is shown in the circuit diagram given in alternative C. The student should insert an object that can allow electricity to pass through it. A nail is made of iron. Since iron allows electricity to pass through it, nail is a good conductor of electricity. In order to complete the circuit, the student should connect the open ends of the wires with a nail of sufficient length. Although the lead of a pencil is encased within a wooden frame, it allows electric current to pass through. Since the given pencil is sharpened from both ends, it can conduct electricity. The bulb can glow only when two terminals of an electric cell are connected to two terminals of a bulb respectively. In such arrangements, a circuit is termed as closed circuit. An electric device such as a bulb works in a closed circuit only. It can be observed that the terminals of the cell and the bulb are correctly connected in arrangements Iand IVonly. Hence, cir cuit arrangements Iand IV are  correct  and  the  bulb will glow. The pictorial representation of the electric cell is represented in the given figure.

It can be observed that an electric cell has two terminals called positive terminal (+) and negative terminal (“). The metal cap attached to one end of the cell is its positive terminal. The path along which electric current flow is called an electric circuit. Non metals like glass, plastic, wood, paper, cloth and rubber are the non-conductors of electricity. Both the statements are true. In series, total emf = sum of the individual emfs = 2 + 2.5 + 4 = 8.5 V www.betoppers.com

6th Class Physics

120 20. 21. 21.

In parallel, emf always remains constant. In series, total emf = sum of the individual emfs = 1 + 1 + 1 = 3v Electric cell

that consists of bell 2, the two terminals of the electric cell are connected to one terminal of the bulb and one terminal of bell 2 respectively. Also, the bulb and the bell are connected to each other and the switch is closed. Hence, the bulb will glow and bell 2 will ring and produce a sound.

SUM MATIVE WORKSHEET 1.

2. 3. 4. 5. 6.

7. 8. 9. 10. 11.

Electric current from cell flows from positive terminal to negative terminal outside the cell through circuit. Electric bulb. No. pure water is an insulator, but salty water is a conductor of electricity. Electric current flows in one direction only. Metal cap. Cells are not placed properly. Positive terminal of one cell is to be connected to negative terminal of another cell. A device that is used to break an electric circuit is called Switch. An electric cell has two terminals. Unit of electric current is Ampere. i - b, ii - a, iii - c i - b, ii - a, iii - c

5.

6.

HOTS WORKSHEET KEY 1 2 B D 11 12 C A

3 4 5 6 7 D B A B A 13 14 15 A B C

8 9 10 C C D

7.

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

2.

3.

4.

In an electric torch, electric cells are the source of current. Without electric cells, it is impossible to construct a torch. In an electric torch, current is produced by the 8. battery. Current passes into the bulb filament through the switch. Hence, current flows through switch, battery, and the bulb filament forming a circuit. Current does not pass through the reflector because it is not a part of the circuit. The bulb glows when current flows through it. On closing the switch, the circuit gets completed. Hence, current flows from the cell through the bulb. Current flows through the circuit only when the circuit is complete. A circuit that has no break is called a closed or a complete circuit. In the circuit

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A nail is made of iron, which is a good conductor of electricity. It allows the current to flow through it. If the free ends of the circuit are connected with the iron nail, then the circuit becomes complete. A current starts to flow in the bulb, and hence, it starts glowing. Hence, Suraj should use the nail to connect the free ends. The bulb of the circuit that is closed will glow. One terminal of the cell of the circuit, which consists of bulb 2, is connected to one terminal of the bulb and the other terminal of the cell is connected to a safety pin. The circuit is complete because safety pin is made up of iron which is a good conductor of electricity. Therefore, bulb 2 will glow. The bulb through which current will flow will glow. Current flows only through a complete circuit. In the circuit constructed by Raju, bulb 1 and bulb 2 are connected in open circuit because the wire is cut in this sub-circuit. Hence, no current will flow through bulb 1 and bulb 2. The current will flow only through bulbs 3, 4, and 5. The direction of current that externally flows through a closed circuit is from the positive to the negative terminal of the cell. Since the current is flowing from terminal M to terminal N of cell I, terminal M must be a positive terminal. Again, it is clear from the second circuit that the current is flowing externally from terminal S to terminal T of cell II. Hence, terminal T must be a negative terminal. The following table shows the nature of the terminals of the given cells.

Electricity Solutions

121 11.

Terminal

Nature

M

Positive

N

Negative

S

Positive

T

Negative

12.

13.

9.

Hence, terminals M and T are positive and negative respectively . Current flows in a closed circuit externally from the positive to the negative terminal of the cell. Hence, current will flow in the given circuit, along the direction as shown in the following figure. 14.

15.

10.

Reflector (curved metallic surface that surrounds the bulb) is a device that is used in a simple torch to focus the emitted light in a particular direction. It is not a part of its circuit and, hence, it does not complete the electric circuit of the torch. Bulb of the given circuit will glow if a conducting object is inserted between ends M and N. Key and nail are made of iron which is a conducting material. Hence, the bulb will glow if Raj would insert key and nail respectively. Bulb will glow only when the circuit is closed. This is possible only when a conducting object is inserted in between the gaps of the given circuit. Since a key is made of iron that allows electricity to flow through it, it is a conducting object. Hence, key can be inserted tightly in the gap to make the bulb glow. Torch is a simple electric device that gives off light. It consists of a bulb that emits light by drawing electric energy from the electric cells that are enclosed in a cylindrical metallic case. Hence, the electricity required for the operation of the torch is provided by the electric cells. A bulb glows only if the current flows through its filament. It is possible only if its two terminals are respectively connected to the two terminals of the cell. Electricity is provided to an electric bulb through both its terminals only as shown in the following figure.

It is clear from the circuit diagram that the directions of current in the wire segments RV, VT, ST, and RS are   respectively.. A bulb glows only if current flows through its filament. It is possible only if its two terminals are connected respectively with two terminals of the cell. An electric cell produces electricity through its two terminals only. Hence, if the free ends of the circuit are respectively connected to the This arrangement is shown in the given diagram terminals IV and I of the cell, then the bulb would labelled as T only. Hence, electricity would flow glow. This is shown in the following figure. through the filament of the bulb in arrangement T only and, hence, the bulb would glow.

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6th Class Physics

122

IITJEE WORKSHEET 1 2 3 4 B A A A 11 12 13 14 B A B C 21 22 ABC ABC

5 6 7 8 9 10 A A A A A A 15 16 17 18 19 20 D A B B B BC

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 23.

24.

i = 10 A t = 10 × 60 sec. Q=? Q = it = 10 × 10× 60 = 600 C Q = 100 C. t = 4 sec

Q 100   25 A . t 4 Q = 10 C i = 2A t=? Q = it i

25.

(or) t  26.

27.

Q 10   5sec i 2

i = 5A t = 5 min = 5 × 60 =300 sec Q = it = 5× 300 = 1500 C Q = 60C t = 4 sec i=?

i

Q t

60  15A 4 Not relevant A  Q; B  P; C  R A  s; B  r; C  p; D  t A  q; B  r; C  p A  r ; B p ; C q 

28. 29. 30. 31. 32.

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Electricity Solutions

123

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6th Class Physics

124

6. MAGNETISM SOLUTIONS 10.

FORMATIVE WORKSHEET 1 D 11 B

12. 15. 18.

2 A 12 *

3 C 13 D

4 C 14 *

5 D 15 A

6 B 16 A

7 A 17 *

8 9 B AC

10 A

2 D 12 C

3 A 13 D

4 C 14 A

5 C 15 A

6 A 16 *

7 CD 17 A

8 D 18 A

19.

9 10 A D 19 A

4 5 6 7 8 9 CD A D B B A

Directive property. Repulsion is the surest test of magnetism. Electromagnet is a strong and temporary magnet. Attractive property of magnet is more at it ends. South Iron, Steel, Alnico. South and North. Removal of inducing magnet. Magnets have both attractive and directive properties. If ‘A’ is a magnet material, and ‘B’ is a magnet there is a attraction when it is brought close to ‘A’. Hence spring extends.

HOTS WORKSHEET 1.

geometric length = 6K and magnetic length = 5K 1 2 3 4 5 6 * C D C C C

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7 8 9 C C C

2 

2 2M ×m =  

IITJEE WORKSHEET 1 A 11 B 21 AB

2 B 12 B 22 ABC

3 D 13 C 23 AC

4 C 14 D 24 AB

5 A 15 A 25 ABCD

6 B 16 C 26 A

1 d2

29.

U se F 

30.

A

Use F  m 1m 2

31.

D

U se F 

32. 33. 34. 35. 36. 37. 38. 39.

A B 3 5 A – q ; B –t ; C – s A – t ; B –s ; C – q; D – q, r A – q ; B –p ; C – s A – b ; B –c ; C – a

SUM MATIVE WORKSHEET

10. 11. 12. 13. 14. 15. 16. 17. 18.

2 

1  New magnetic moment, M = 2×

Magnetic field

1 2 3 A A C

 r=

 New length of the magnet = 2r = 2×

CONCEPTIVE WORKSHEET

16.

2 = r

(i)– A; (ii) – B; (iii) – B (i) B (ii) D (iii) A (i) A ; (ii). D ; (iii) C

1 C 11 A

When the magnet is bent into a semicircle its length

1 d2



7 C 17 A 27 B

8 B 18 C 28 B

9 A 19 A 29 D

10 B 20 B 30 A

7. HEAT SOLUTIONS

FORMATIVE WORKSHEET KEY 1 2 3 4 5 6 7 B D C C D B D 8 9 10 11 12 13 14 C C B B C A D HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1. The sense of touch in our body helps in distinguishing cold, warm and hot body. 2. The effect of heat are (a) All matter expands on heating (b) Solids expand on heating. (c) Substances expand on heating; this expansion is different for different substances. (d) Liquids expand on heating. Different liquids have different rates of expansion for the same rise in temperature. (e) Gases also expand on heating. Expansion in gases is very large as compared to the solids or liquids. 3. The S.I. Unit of temperature isKelvin 4. The fastest mode of transmission of heat is radiation. 5. Black surfaces are good absorbers and good radiators of heat. 6. Copper expands more and bends on iron strip 7. Wood is the bad conductor or elecricity. 8. Stainless steel pans are usually provided with copper bottoms. The reason for this could be that copper is better conductor of heat than the stainless steel 9. Thermos flask 10. Silver > Copper > Aluminium > Iron > Lead 11. i - d, ii - a, iii - b 12. i - c ii - d iii - b 13. i - b ii - a iii - c 14. i - d ii - c iii - b

CONCEPTIVE WORKSHEET

1. 2. 3. 4.

5. 6. 7. 8.

9. 10.

SUM MATIVE WORKSHEET 1.

2.

3.

4.

5. 6.

KEY

1 2 3 B D A 6 7 8 C D C

4 5 D A 9 10 B D

HINTS/ ANSWERS TO THE SELECTED QUESTIONS A body losing gaining feel hot. The flow of heat is rapid when there is a big difference in the temperature of two bodies The degree of hotness or coldness of a body is called temperature. As the tranfer of heat takes place from hot water to colder water, the temperature of the mixture would be between 30°C and 90°C. Heat will flow from cup to water Normal temperature of human body is 37°C or 98.4oF (D) Transfer of heat through the movement of particles of the medium from one place to another is called convection. It occurs in liquids and gases (fluids). Radiation All

7.

This is because the sensation of touch is relative. When we shift over hand from cold water to tap water our cold hand starts gaining heat and we feel tap water to be hot. Thermometer is a simple device used for measuring the temperature of an object or a body. • Cooking utensils are made from metals. This helps in fast cooking of food. • Copper is used for coating on the bottom of some steel utensils to help uniform and smooth transfer of heat from the flame to the food being cooked. • Mercury is used in thermometers since it is a good conductor of heat. In between two wall thermocol or PUF is filled which acts as an insulator. This prevents the flow of heat from outside into the refrigerator. Poor conductors of heat. There is an extra layer of air trapped between thin blankets which acts as an insulator and does not allow the heat from the body to flow out. Convection currents in gases.

6th Class Physics

126 8.

9. 10.

Proportional to the distance between the source of heat and the recipient of heat. Eg: If you get away from fire, heat radiation reaching you is relatively less. Because smooth and shining surfaces are poor absorbers and poor radiators of heat. Vertically upwards.

HOTS WORKSHEET 1.

2.

(a)

Temperature

(b)

Energy

(c)

Joule

(a)

False. It s the measurement of hotness

8.

Ans: (a) 9.

10.

True.

(c)

False. Temperature is measured in

Celsius or Fahrenheit Scale. (d) 3.

True.

Heat always flows from a body at higher temperature to lower temperature.Heat energy will flow from our body to the surroundings if the surroundings are at a lower temperature than our body.

11.

12.

when they are in contact with each other. b) Convection: This method by which heat is

13.

transferred by the mass movement of the liquid or gas itself is called convection. c) Radiation : Radiation is the form of heat transfer that can occur in the absence of a medium. 5.

Conduction, convection, and radiation are different modes of heat transfer. Ans: (b)

6.

Convection does not occur in Vacuum. Ans: (a)

7.

In fluids, heat transfer takes place primarily due to convection. Ans: (b)

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(b)

Radiation

(c)

Conduction

(d)

Convection

(e)

Conduction

(a)

Conduction

(b)

Radiation

5 A 10 D 15 3

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 10. (D) We know that C = 5/9 (F – 32) = 5/9 (86 – 32) = 5/9 × 54 = 30 Therefore, 86 °F = 30 °C

a) Conduction : Conduction of heat energy can occur within a body or between two bodies

Convection

1 2 3 4 C C A D 6 7 8 9 ABC A BCD AB ABCD 11 12 13 14 A C B 100

Ans: (c) 4.

(a)

IITJEE WORKSHEET

or coldness of a body. (b)

Wool is the bad conductor of heat.

14. 15 16. 17. 18. 19.

(A) We know that F = (C × 9/5) + 32 We are given that C = 45, Fahrenheit = (45 × 9/5) + 32 °F = (81+ 32) °F = 113 °F (C) Fahrenheit = (35 × 9/5) + 32 °F = (63+ 32) °F = 95 °F (B) C = 5/9 (41 – 32) = 5/9 × 9 = 5°C 100° C 3 A r ; B t ; C  d ; s  p ; D q A s ; B p ; C  q A  r, p ; B  s ; C  q A s ; B r ; C  q