Matter, Energy, and Radiation: A Syllabus for Science A1, the First Semester of a Two-Year Course in Science in Columbia College 9780231886260

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MATTER, ENERGY, AND RADIATION

MATTER, ENERGY,

AND

RADIATION A Syllabus for Science Al, the First Semester of a Two-Year Course in Science in Columbia College

J. R. DUNNING H. W. FARWELL

NEW YORK: MORNINCSIDE

COLUMBIA

HEIGHTS

UNIVERSITY

1935

PRESS

C O P Y R I G H T 1935 COLUMBIA UNIVERSITY

PRESS

P U B L I S H E D 1935

L I T H O G R A P H E D IN T H E I ' X I T E D STATES O F AMERICA

Preface This Syllabus has been prepared for students in Soience Al, the first semester of a two-year sequenoe in the sciences in Columbia College. Ώιβ oourse Soience Α-B is designed for those studente who do not intend to use the eoienoes professionally, but who desire a general acquaintance with the ohief fields of scientific investigation - a discussion of their dominant problems, concepts, and theories, and an introduction to the techniques of experimental methods. Its aim is to present as systematically as possible those themes of modern soience that are of general interest and significance. The opportunity is open for the student to go as far as he wishe3. The oourse is conceived as a unified program of study for students who desire to satisfy the scienoe requirement for the Baohelor of Arts degree. The major topics of the two-year program are shorn on the following pages. This Syllabus for Sçienoe Al is not intended to serve as a text, but rather as a guide to the students' thinking, foousing their attention on the three topics: MATTER, ENERGY, and RADIATION, emphasizing the important sub-topios, and opening up the more vital questions in the various fields, rather than going into the smaller details. There is no definite textbook for Soienoe Al, although Lemon, "From Galileo to Cosmio Rays," and Loeb and Adams, "Development of Physical Thought" are used as the prinoipal reference texts. In order to take advantage of the opportunities offered by the course, the student is urged to read widely from the list of Essential and Suggested Readings, placed at the end of eaoh week's seotion of the Syllabus. The special oolleotion of books and periodicals in the Soienoe Reading Roam is shown at the end of the Syllabus. For the laboratory the class is divided into as small sections as possible. In each laboratory period an attempt is made to oover a number of significant experiments, some of which are quantitative and some of a qualitative nature. In same oases the experiments are performed individually, but in many oases they are performed by the group as a whole under the guidance of the instructor. This method makes possible an experience for the student whioh the conventional individual experiment cannot afford. The laboratory work is supplemented by visits to the Hayden Planetarium, the Rutherfurd Observatory, and the various researoh laboratories in this and other departments. An opportunity for a certain amount of special individual work will be provided. The suggestions and assistance of the other meirbers of the conmittee in charge of the science course, and of the members of our own department, have been very valuable in preparation of this Syllabus. J. R. Dunning H. W. Farwell Pupin Physics Laboratories Columbia University August, 1935

Contente General Outline of Two-Year Science Course First Week.

Seotion I.

Second Week.

GENERAL INTRODUCTION

Section II.

MATTER

ix 1 5

Three States of Matter. Properties of Matter: Mechanical, eleotrical, etc.

Third Week.

Seotion II.

MATTER (continued)

8

Physical and Chemioal Properties. Atomic Theory.

Fourth Week.

Seotion III.

ENERGY

11

Energy - a Purchasable Commodity. Mechanical Energy. Fifth Week.

Section III.

ENERGY (continued)

14

Prinoiple of Conservation of Energy.

Sixth Week.

Seotion III.

ENERGY (oontinued)

18

Electrical Energy - Production and Conversion. Conservation of Energy and Transformations. Seventh Week.

Section III.

ENERGY (continued)

22

Particle Nature of Matter. Kinetio Theory of Matter - Gases.

Eighth Week.

Section III.

ENERGY (continued)

27

Kinetic Theory - the Gas Laws. Gases, Liquids, and Solids. Ninth Week.

Section III.

ENERGY (oontinued)

Kinetio Theory. Continuity of State. Thermal Cycles. Struoture in Matter.

32

C O N T E N T S

•iii

Tenth Week.

Section IV. RADIATION

37

The Electron - Ite Properties. Electrical Cirouits. Conduction in Gases. Eleventh Week.

Seotion IV. RADIATI OK (continued)

45

The Eleotron. Photoeleotric Effect. Thermionic fisiseion. Electromagnetic Radiation - Radio. lVfelfth Week.

Seotion IV.

RADIATION (continued)

49

Temperature Radiation - Quantum Theory. Radiation from Exoited Atoms. Spectroscopy. Thirteenth Week.

Seotion IV. RADIATION (continued)

53

X-rays - Crystal Analysis. Electromagnetic Radiation. Fourteenth Week. The Nucleus.

Seotion IV. RADIATION (continued)

57

Radioactivity.

Soience Reading Room and Book Collection

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General Outline of the Course Science A-B In order to provide a comprehensive view of the scope of the whole course, these four brief outlines for Science Al, A2, Bl, B2 indicate the major topics of the four semesters.

SCIENCE Al MATTER. ENERGY. AMD RADIATION I.

GENERAL INTRODUCTION Science and civilization. What do ne mean by soienoe? The importance of experiment.

II.

MATTER The three states of matter - solid, liquid, gas. State is an aooident of temperature and pressure. Physical properties. Density, meohanioal, thermal, optioal, eleotrical, etc. Physioal and ohemioal phenomena. Elements, oompounds, and mixtures. The atomic theory. General atomio structure, nucleus, external electrons.

III.

ENERGY The oonoept and measurement of energy. A purchasable commodity. Meohanical energy. Foroe and distanoe. Potential and kinetio energy. Energy conversions. Prinoiple of Conservation of Energy. Application to all forms of energy - heat, eleotrioal, eto. Transformation of energy into various forms. The basis of modern civilization. The partióle nature of matter. Atomio structure and the Periodio Table of Elements. The kinetic theory of matter. (Gases, liquids, and solids.) Structure in matter - crystalline and non-orystalline. Statistical nature of kinetio theory and theories in general.

IV.

RADIATION The electron. Electrioal circuits, discharge in gases, P.E., etc. Thermionic emission, electromagnetic radiation. Temperature radiation. Planok's quantum hypothesis. Spectra. Spectral lines and series. The Rutherford-Bohr atom. The quantum theory. X-rays - crystal analysis - atomic structure of matter. Electromagnetic radiations: Radio - cosmic rays. The partiole-wave controversy. The nucleus - a new era in physios. Isotopes and radioactivity. Nuclear transformations, and nuolear energy. The equivalence of matter, energy, and radiation.

GENERAL OUTLINE OF SCIENCE Λ-2

χ

SCIENCE A2 CHB1ICAL CHARGES IK MATTER I.

ELEMENTS. CCMPCUNDS. and MIXTURES The elements and chemical reactions. Oxygen, hydrogen, and water. Atoms and molecules - reviewed. Chemical formulae, equations, valence. The atmosphere and its components. Use of the Periodic Table of the Elements.

II.

SOLUTIONS Concentration and saturation, pressure and temperature. Ionization. Acids and bases.. Neutral ization. Eleotron transfer. Oxidation and reduction. Colloidal solutions.

III.

CHEMICAL EQUILIBRIUM Rates of reactions. Nitrogen fixation.

IV.

Reversible reactions.

SOME GROUPS OF THE ELEMENTS Halogens, sulfur, phosphorus.

V.

THE METALS Alkalies and alkaline earths. Aluminum and iron. Metallurgy. Electrochemistry. Alloys - other metals.

VI.

CARBON COMPOUNDS The carbon atom, structural formulae, isomerism. Hydrocarbons. Combustion. Carbohydrates and photosynthesis. Alcohols, acids, and esters. Fermentation. Fats and proteins. Putrefaction.

VII.

FOODS Nutrition. The vitamins. Introduction to biological methods in chemistry.

GENERAL OUTLINE OF SCIENCE Α - B SCIENCE B1 THE EARTH, ITS ORIGIN AMD PHYSICAL HISTORY I.

INTRODUCTION

II.

ASTRONOMICAL ASPECTS The u n i v e r s e .

III.

The g a l a x y .

The s o l a r system.

THE EARTH AS A PLANET General f a c t s . Time. The moon. Map p r o j e c t i o n s .

IV.

THE EARTH AS A GEOLOGICAL BODY The c r u s t of the e a r t h . Minerals. Rocks.

V.

GEOLOGICAL PROCESSES Weathering. Streams. Underground p r o c e s s e s . G l a c i e r s . Waves. Wind.

VI.

GEOLOGICAL STRUCTURES Horizontal s t r u c t u r e s . Domed s t r u c t u r e s . Faulted s t r u c t u r e s . Folded s t r u c t u r e s . Complex s t r u c t u r e s .

VII.

REGIONAL GEOLOGY The United S t a t e s .

V I I I . HISTORICAL GEOLOGY The g e o l o g i c a l column. Evolution. Pre-Cambrian g e o l o g y . The P a l e o z o i o . The Mesozoio. The C e n o z o i c . The e v o l u t i o n of man.

xi i

GENERAL OUTLINE OF SCIENCE A-B SCIENCE B 2 TRANSFORMATIONS OF MATTER AMD ENERGY IN LIVING ORGANISMS

I.

INTRODUCTION Survey of plants and animals. Similarities in structure and function.

II.

LIVING MATTER Chemical composition. Elements - compounds. Dynamio constituents - Enzymes. Basic processes. Diffusion, osmosis, catalysis. Sources of materials in nature.

III.

SOURCES OF ENERGY IN LIVING ORGANISMS The green plant. Structure. Photosynthesis - osmosis, enzyme action. Growth - reproduction, heredity, and evolution in plants•

IV.

UTILIZATION OF ENERGY IN MAINTENANCE Metabolism. Digestion, distribution. Respiration - excretion. Food and energy cycles. Sensory activity. Coordination - movement. Stimulus and response. The adjustory system - nerves.

V.

UTILIZATION OF ENERGY IN ADVANCING PROCESSES Growth. Cell division. Embryology. Physiology of development. Reproduction. Asexual and vegetative. Sexual - chromosomes. Reproductive organs. Heredity and evolution. Mendel 's law. Heredity and environment.

VI.

INTERDEPENDENCE OF PLANTS AND ANIMALS Food cycles. Bacteria. Ecology.

VII.

HUMAN BIOLOGY

First Week SECTION I - GENERAL INTRODUCTION A. SCIENCE AND CIVILIZATION Why is science so important for the eduoated man of today? In what respect is soienoe valuable to sten who are not to be professional scientists? In subject natter, as suoh? In method? Or in both? No matter what field you enter, why oan you be certain that the past and future developments in soienoe will greatly influence your work and thought? What is the fundamental idea behind this offering of a two-year scienoe program? The program for the four semesters, whose major topics are shown on pages ix-xii, offers you an opportunity to become acquainted with the chief fields of soientific investigation, with their dominant problems, conoepts, and theories, and with the teohniques of their experimental methods. What are the sciences, and how did the arbitrary distinctions arise? Was Galileo a physioist or an astronomer? Was Newton a mathematician or a physioist? Is the trend toward further specialization and sharply separated fields in scienoe, or is there a trend toward a realization that the same bas io principles underlie all the soienoes? If there has been a development of our civilization, wherein has soienoe played a part? Is science likely to beoome a still more important factor in the future, and exert a more profound influenoe on our sooial, industrial, and politioal order, or has science reached the peak of its influence? Suoh questions as these can hardly be answered by any one man, but in the consideration of them we oan acquire a greater understanding of the world in whioh we live, the oiroumstanoes which have led to our present conditions, of our contemporary problems, and of some of the possibilities whioh the future offers. B. WHAT DO WE MEAN BY SCIENCE? Before we go far into any one field we ought to have some understanding of this question. In a sense, scienoe is a produot of man's curiosity, of his imagination, and often of his pressing need. Man's desire to understand the nature of the world around him, his long searoh for ideas and for truth have not produced merely a dead set-of faots, but a living, fascinating drama whioh has really only begun.

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Β. CONTINUED Arbitrary definitions are rather dangerous, and we nay understand what we mean by science better through considering the way in whioh a science oomes into existenoe and grows. For example: How did the earliest machines come about? How did geometry develop from the "rope stretchers" in Egypt? Better still, consider the gradual development of our ideas of the solar system, beginning with man's first wonderment at day and night, through the development of early and modern astronomy, on up to our current notions about expanding universes. Rise of astronomical knowledge. An example of the growth of scienoe. Early superstitions. What ideas did the oave men have? Beginning of observation. What part did religion, the early priests and astrologers play in beginning experimental observation? How far did the early civilizations, suoh as the Babylonian, go ? The Greek School. Why has the long line of Greek thinkers from Thaïes and Pythagoras on down to Aristotle had suoh an influence? What led to the general acceptance of the geooentric theory? The interim of seventeen centuries. What factors played a part in arresting the growth of soienoe during the seventeen centuries from the Greek School to Copernicus? Are such factors still operating in the world today? The beginning of modern scienoe. Why has the development of the experimental method through the work of Copernicus, Galileo, Tycho Brahe, and others been so important, and had so many repercussions in other fields of human activity? What are the basic facts of the solar system? How does the work of Tyoho Brahe, Kepler, and Newton illustrate the effectiveness of a combination of theory and experiment? The planets. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune (with their various satellites or moons) traverse elliptical orbits, with the sun at one of the foci, the ellipses being nearly in the same plane. Kepler. The distances range from about 36 million miles for Mercury, to about 2790 million miles for Neptune. The Earth is about 93 million miles from the sun, has a period of about 365 l/4 days, and a radius of about 4000 miles, while its satellite, the moon, is about 240,000 miles distant and has a period of about 27.3 days. The squares of the times of revolution of the planets are proportional to the cubes of their mean distances from the sun. T*/v r s . - Kepler.. The straight line joining the sun to a given planet, (radius vector), moves so it sweeps out equal areas in equal periods of time. - Kepler. The planets move in equilibrium between the gravitational attraction force F » lonm'/r* toward the sun and the

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Β. CONTINUED oentrifugal foroe outwards, F • mr'/r. These concepts and developments from them will be considered more fully In Soienoe Bl. In what ways does the work in the fields of physios, chemistry, and mathematics, by Newton, Leibnitz, Boyle, Huyghens, laplace, and others. In its reaotion on astronomy, show the interdependence of all fields of scienoe? Modern astronomy and astrophysios. Our growing picture of the universe - the stars, galaxies, nebulae - expanding universes, relativity. Hale, Hubble, Tolman, Einstein, LeMaitre, and others. The future - our knowledge of the universe only beginning. The cooperation of physics, chemistry, geology, mathematics. Does this development of astronony consist simply of ever-increasing accumulation of facts? How does this brief survey of one science help us understand what we mean by science? C. THE RÔLE OF EXPERIMENT What is an experiment? Why does the.substitution of oontrolled quantitative experiments, for wild ideas partly or wholly unrelated to facts and for frequently misleading hit-or-miss happenings, represent such a great step forward? To what extent have we actually taken advantage of the soientific method in other contemporary human undertakings? How do theories grow out of the results of experiment? What is the . rôle of theory in science? Why must an aocepted theory rest fundamentally on results of experiment? How do experiment and theory go hand in hand in much of our scientifio work? In what ways do the possibilities of experimentation differ widely In the various sciences? IN THE LABORATORY Speoial Visit to Hayden Planetarium As an introduction to science, Dr. Clyde Fisher of the American Museum of Natural History has arranged a speoial program for us at the Hayden Planetarium, 77th Street and Central Park West. The dates for this visit will be announced. What types of phenomena connected with the solar pystem and the universe is the Zeiss Planetarium projector capable of showing? Rutherfurd Observatory. Regular Laboratory Period At the first regular laboratory meoting Professor Schilt and the Astronomy Department have provided an opportunity to visit the Rutherfurd Observatory on top of the Pupin Physics Laboratories, in order to study the equipment of the observatory, the large refractor telesoopes, with equatorial mountings, the transits, and the various other tools of the astronomer.

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On one or more evenings during the week (to be announced) we have been invited, weather permitting, to view some of the stars and planets through the 12-inch refraotor. FOR STUDY AMD READING ESSENTIAL Loeb and Adams, "Development of Physioal Thought," pp. 1-54. Or Knowlton, "Physios for College Students," pp. 1-11, 65-73. Or Lemon, "From Galileo to Cosmio Rays," pp. 3-8, 12-31. SUGGESTED Fath, "The Elementa of Aetronony." Lenard, "Vîreat Men of Science." Lodge, "Pioneers of Science," chs. 3, 4, 5, on Galileo. Mayer, "Seven Seals of Scienoe," p. 211. Newman (Moulton), "Nature of the World and Man." Sedgwiok-Tyler, "Short Hietory of Science," p. 191.

Second week SECTION II - MATTER A. INTRODUCTION All soienoes primarily study natter In its various forms and relationships, and nearly all human activities have definite dependenoe on matter and its properties. Henoe we ought first to find out as suoh as possible about our working materials. Matter may exist in three fundamental states, gas, liquid, or solid. Can all substanoes exist in all of the three states? How do temperature and pressure determine the state of any given substance? With what advantages in this respect have our aocidental oiroumstanoes provided us Τ Suppose our average temperature were 30°C lower? 30°C higher? How much of a change in average temperature would it take to oause another ice age? How muoh do we know about the behavior of matter at the lowest temperatures obtainable? B. PROPERTIES OF MATTER Let us oonsider some of the typical properties whioh make it possible to distinguish one kind of matter from another. Density differences are quite marked. Density • Weight per unit volume » W/V. How are the basic unite of C.G.S. (oentimeter-gram-seoond) system defined and used? Why does the scientist need exaot definitions? Meohanioal Properties. Elasticity, malleability, ductility, hardness, strength, viscosity, etc. provide a basis for distinction. Are all of these properties found in all states of matter? Do all substanoes follow Hooke's law, F = -kx ? How much does industrial progress depend on the mechanical properties of matter, and the development of special materials with special properties? What about aluminum, stainless steel, rubber, bakelite? What other special materials are needed today? Structure in Matter. Large differences in structure exist, from the orystalline to the 6o-called non-crysta11ine forms, but actually all matter has structure. How small can we subdivide a piece of matter and still have it preserve its characteristics? Thermal Properties. Such thermal properties as conductivity, melting point, boiling point, and expansion with change of temperature are highly important. Can we improve on the thermal properties of materials found in nature? Heat insulators?

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CONTINUED The boiling pointe range all the way from -269°C for helium to 5900°C for tungsten. Optical Properties. The index of refraction, the transparency and color of materials are involved in fundamental problems. Are each of these properties independent? For example, does the index of refraction depend on colorì Electrical Properties. The electrical conductivity, for example, varies from nearly zero for such materials as amber, to nearly infinity for superconducting metals at very low temperatures. Would you expect electrical and thermal conductivities to be related? Does the fact that the conductivity of a material is a constant independent of the current flowing (Ohm 1 s law R » v/l) seem fortuitous? This is an incomplete, but typical, list of properties, some general, some specific, which enable us to describe matter. In order to understand these properties of matter in bulk, we must go deeper, to the particles of which matter is built, the molecules, the atoms themselves, and even the eleotrons and the other component parts of the atoms. IN THE LABORATORY ι can we measure some of these typical properties of various materials? Density. In order to beoome familiar with some typical materials in nature, and methods of measurement, make use of simple methods based on correct definitions to determine the density W/V of a wide range of materials: Gases: CO*, air (N, and 0 t ) and H or illuminating gas; various liquids and solids. Can you suggest other methods of measuring density which would be applicable? Determine as many other properties of the substances available, such as color, hardness, etc. which individual inspection will disclose. Mechanical Properties. Test the mechanical properties such as hardness, flexibility, breaking strength, etc. of a number of materials with the apparatus available. From your measurement of the tensile strength of steel wirea compute the breaking strength of one of the 36-inch cables of the George Washington bridge. Structure. Examine directly, and und'är microscopes with various magnifications, a sufficient variety of samples to learn something about crystalline structure.

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Do all of tho materials oxamined have structure? What forms can you definitely identify? ΡΟΚ STUDY AND HEADING ESSENTIAL Lemon, pp. 91-105, 109-115, 177-184, 191-196, 265-268. Or loeb and Adams, pp. 74-90, 19L-206, 317-322, 418-421. SUGGESTED Joffe, "Physios of Crystals." Knowlton, pp. 131-142. Saunders, pp. 305-310.

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Third Week SECTION II - MATTER (Continued) C. PHYSICAL AKD CHEMICAL PROPERTIES Why do we distinguish between physloal and ohemloal phenomena? Is this distinction real, or somewhat arbitrary? Should the physicist or the ohemist study the conduction of e l e c t r i o i t y through metals? Through solutions? Through gases? With what properties of matter is the ohemist c h i e f l y concerned? How do we know whether a given lump of material ia a mixture. a compound. or an element? Is the d e f i n i t i o n of an element given by Boyle in the "Sceptical Chymist" satisfactory now? Does the oonoept of atoms seem essential in desoribing ohemloal processes involving the ohanges in composition and energy which oocur when elements interact with eaoh other? D. THE ATOM Should we c a l l the early suggestions of Democritus and Leuclppus, that matter is oomposed of elementary p a r t i c l e s , more than pure speculation? Why was the general aoceptanoe of the atomic nature of matter delayed until a f t e r the disoovery of radioaotivity, by Becquerel, in 1896, even though the e a r l i e r experimental work of Dalton, Gay Lussac, and Avogadro on gases had clearly indicated the existence of atomst What do we mean by an atom? Is the word etymologically oorrect now? Are single atoms (about 10-8 cm in diameter) v i s i b l e under a microscope? Can we prove by other methods that atoms r e a l l y exist? I f i t i s so small, why should we be able t o detect by e l e o t r i c a l methods the nucleus of a single helium atom (alpha p a r t i ó l e ) when i t i s ejected from radioactive elements? The 93 major kinds of atoms, or elements. Are some s t i l l unknown? Note the arrangement in the Periodio Table of the elements, of whioh more l a t e r . In what respects do these 93 types of atoms d i f f e r ? For an example, how i s an iron atom (Fe) d i f f e r e n t from an aluminum atom? How muoh do we know about the internal structure of atoms of the various elements? Simple Concepts of Atomic Structure. Roughly analogous t o the solar system, g The simple H (hydrogen) atom, about 10 om diameter. Central nucleus - proton - mass about 1.007 units. 1.66 χ 10-24 gm, about 10 - 1 3 om "radius." single + charge.

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D. CONTINUED E x t e r n a l " p l a n e t a r y " e l e o t r o n . mass 1/1840 p r o t o n . single - charge. A dvnamlo atom m o s t l y empty s p a c e . Atomic number = Number of e x t e r n a l e l e o t r o n s = n o . p r o t o n s i n n u c l e u s , t o be e l e c t r i c a l l y b a l a n c e d . Atomic number of H = 1 , of U (uranium) = 9 2 . Atomio w e i g h t : w e i g h t of atom ( l a r g e l y due t o n u c l e u s ) on a r b i t r a ry s c a l e , with o x y g e n ^ = 16.0000. Atomic w e i g h t of H = 1 . 0 0 7 , of U = 238. Why must a l l t h e p r o p e r t i e s of m a t t e r , p h y s i o a l , c h e m i c a l , b i o l o g i o a l , e t c . depend u l t i m a t e l y on t h e c h a r a c t e r i s t i c s of t h e s e atoms and their constituents? How do we make c h e m i c a l c o m b i n a t i o n s of t h e s e atoms? Do t h e y a l l form c o m b i n a t i o n s ? Do atoms d i f f e r i n t h e way t h e y form c o m b i n a t i o n s w i t h o t h e r k i n d s o f atoms? Moleoule: A c o m b i n a t i o n of two o r more atoms of t h e same kind suoh as 0 , , N t , e t c . , o r of atoms of a d i f f e r e n t k i n d , suoh a s CO t , Η,Ο, e t c . Are o r d i n a r y p h y s i c a l p r o o e s s e s v i o l a t i o n s of t h e P r i n c i p l e of C o n s e r v a t i o n of M a t t e r , i . e . , t h a t m a t t e r can n e i t h e r be o r e a t e d nor d e s t r o y e d ? What about ç r d i n a r y c h e m i c a l t r a n s f o r m a t i o n s ? Have we any e v i d e n c e t o j u s t i f y t h e s a y i n g t h a t a l l m a t t e r i s f u n d a mentally e l e c t r i c a l in nature? IN THE LABORATORY Physical Mixtures. What i s a p h y s i o a l m i x t u r e ? What methods a r e a v a i l a b l e f o r t h e s e p a r a t i o n of such m i x t u r e s ? Study t h e e f f e c t of g r a v i t a t i o n a l f o r o e i n o a u s i n g m i x t u r e s of f i n e s i l t s , c l a y s , s a n d s , e t c . t o s e t t l e out of w a t e r m i x t u r e s . Does S t o k e s ' law, t h a t t h e r a t e of f a l l of a p a r t i c l e i s p r o p o r t i o n a l t o t h e s q u a r e of t h e r a d i u s of t h e p a r t i c l e d i v i d e d by t h e v i s c o s i t y of t h e f l u i i , seem r e a s o n a b l e ? Why should t h e f i n e r p a r t i ó l e s , a s i n t h e case of t h e gold c o l l o i d , remain suspended i n d e f i n i t e l y ? I s t h i s f a c t c o n n e c t e d w i t h t h e c o n s t a n t m o t i o n of t h e w a t e r m o l e c u l e s ? Centrifuges. Observe t h e a c t i o n of t h o h i g h speed c e n t r i f u g e i n g r e a t l y i n c r e a s i n g t h e r a t e of s e t t l i n g of t h e p a r t i c l e s . What s e t s a l i m i t t o t h i s method ? I f t h e c e n t r i f u g a l f o r e « F = ( W / g ) ( v ' / r ) , how much g r e a t e r t h a n t h e g r a v i t a t i o n a l f o r c e W i s t h e f o r c e F on t h e p a r t i c l e s i n t h e c e n t r i f u g e ? The c e n t r i f u g e r e v o l v e s a t about 4000 RFM, and r = 20 cm. See how e f f e c t i v e p u r e l y p h y s i o a l metnods a r e i n s e p a r a t i n g a p h y s i c a l m i x t u r e of v a r i o u s m a t e r i a l s , such as s a n d , l e a d s h o t , i r o n f i l i n g s , and s a l t .

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Are separations in general completely quantitative? ways fractional?

Or are they al-

Could we use che^iioal methods of separation more effectively? Detecting Single Atoms. After "dark adapting" your eyes, observe the tiny scintillations produced in the zinc sulfide (&iS) screen of the "spinthariscope," and the various microscopes by the individual alpha particles (nuclei of helium atoms) whioh are ejeoted from radium or radium F (polonium). The velocity of alpha particles from polonium (radium F) (about 12,000 miles per second) is «uoh that in spite of their tiny weight of about 6.6 χ 10-24 gms, each single alpha particle has sufficient energy to disturb a molecule of zinc sulfide to such an extent that it produces a tiny burst of light large enough to affect the human eye. Do these scintillations oocur regularly, or at random? What makes your watoh dial glow in the dark? Observe it under the microscope. FOR STUDY AND READING ESSENTIAL Bazzoni, "Energy and Matter." McPherson and Henderson, "General Chemistry," pp. 1-26. Or Loeb and Adams, pp. 245-260. Or Lemon, pp. 316-325. SUGGESTED Crowther, "Ions, Electrons, and Ionizing Radiations." Jauncey, "Modern Physics," pp. 358-363. Mayer, "Seven Seals of Scienoe," p. 239. Rutherford, Chadwick and Ellis, "Radiations from Radioactive Substances," pp. 54-58, 544.

Fourth Week SECTION III - ENERGY A. INTRODUCTION What is energy? What primarily do we buy when we purchase food, electricity, coal, gasoline, or gas? Is energy the most fundamental basis of value? How much of human activities can be put purely on an energy basis? What about energy as a medium of exchange? Sinoe energy is so important and its utilization the foundation of progress and of life, we ought to have a thorough understanding of its nature . B. IDEAS ABOUT ENERGY MECHANICAL ENERGY Why did the concept of mechanical energy develop first? How do we use the expressions Energy = Force χ distanoe (grams χ centimeters or lb χ ft) to measure energy or work? Must the force be in the same direction as the motion? If a force of 150 lb is required to move a 3200-lb car a distance of 20 ft, how much energy has been utilized? Are the units foot-pounds, or gram-centimeters adequate to measure all mechanical energy? Why is the physioist so interested in "units" or "dimensions"? What about other types of forces, such as electrical? POTENTIAL ENERGY With what examples of potential energy, energy stored up, do you come in contact in everyday life? Is the expression: Potential energy = W χ h (gm χ cm or lb χ ft) adequate? Sinoe gravitational potential energy depends on the height h, it is always "relative." What about other forms? A certain gasoline advertises that a gallon of it will lift a 3000-ton locomotive 15 ft. How much potential energy per gallon does this indicate? In what form is it? KINETIC ENERGY How must we use the relation: Kinetic energy = \/Z W/g v* to measure the energy of moving bodies? Does kinetic energy have the same units, gm cm or ft lb, as potential energy ? How are the quantities that enter into the expression defined, and what units do they have? The quantity W/g, i.e., weight/acceleration of gravity, is often called the Mass. g = 980 cm/sec*, or 32 ft/sec1 .

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Β. COKTINÜED Conversion o f Mechanioal Energy. Mechanical t o p o t e n t i a l energy, or v i c e v e r s a . What happens when a book f a l l s from the t a b l e Î Are we j u s t i f i e d in b e l i e v i n g t h a t a l l o f the p o t e n t i a l energy of a body r e l a t i v e t o the ground i s converted into k i n e t i c energy i f i t f a l l s t o the ground? Cars have o c c a s i o n a l l y skidded o f f the 126th S t r e e t viaduct in ioy or wet weather, and plunged about 75 f t t o the s t r e e t below. How much p o t e n t i a l energy did a 4 , 0 0 0 - l b c a r have before the plunge j u s t as i t was poised on t h e edge7 How muoh k i n e t i c energy did i t have as i t h i t the s t r e e t ? What happened t o the k i n e t i o energy? How much o f the mechanical work in industry i s based on conversion o f p o t e n t i a l t o k i n e t i c energy? Where does the energy oome from o r i g i n a l l y ? IN THE LABORATORY How can we measure energy, d i r e c t l y or i n d i r e o t l y , in a c t u a l p r a c t i o e ? What methods do we have for measuring f o r c e ? Does the s t r e t c h i n g o f a spring obey Hooke's law, F = - k x , s u f f i c i e n t l y well so t h a t i t may be used a c c u r a t e l y t o measure force? What about the beam balance, or platform balance? Why do we use machines? I n v e s t i g a t e what happens t o the energy in a number o f d i f f e r e n t machines, such as a pulley system used t o l i f t a heavy weight, an inclined plane, a d i f f e r e n t i a l pulley, a gear system, or automobile transmission. Measure the energy output or work done i . e . , Load χ distance load moves C f t . l b or gm.cm) Measure the energy input i . e . , Force χ distance force moves ( f t . l b or gm.cm) E f f i c i e n c y = Output energy Input energy Where does the " l o s t " energy go? I s i t r e a l l y l o s t ? Is f r i c t i o n ever u s e f u l ? What about car brakes? Measure the v e l o c i t y of a r i f l e b u l l e t by means o f the b a l l i s t i c pendulum. Trace what happens t o the energy of the b u l l e t as i t leaves the gun barrel. Why does not the K.E. o f the block = the K.E. o f the b u l l e t ? At what rate i s the human machine capable of doing work, say when making a standing jump? i . e . , can we get some idea what i t s maximum power or rate o f doing work i s , in f t . l b / s e c , or gm.cm/sec?

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FOR STUDY AND READING ESSSENTIAL Lemon, pp. 5 7 - 6 4 , 6 5 - 7 4 , 8 3 - 9 0 . Or Loeb and Adama, pp. 5 5 - 6 1 , 1 0 9 - 1 2 0 ,

134-138,

SUGGESTED Knowlton, pp. 1 2 - 2 1 , 2 6 - 3 3 , 3 6 - 4 3 . Saunders, pp. 7 9 - 8 6 . Webster, F a r w e l l , and Drew, pp. 7 0 - 8 2 ,

110-112.

178-187.

is

Fifth Week SECTION III - ENERGY

(Continued)

C. PRINCIPLE OF CONSERVATION OF ENERGY Just what does it really mean? Does the total amount of energy involved in physical and ohemioal processes remain constant? MECHANICAL ENERGY How does the principle apply to cases where mechanioal energy is transferred from one form to another, or from one machine to another, as by a chain or belt drive, or through gears? Does the expenditure of a certain amount of mechanioal energy necessarily result in the appearance of exactly that same amount of mechanical energy elsewhere? Conversion of mechanioal energy into other forms. Frictional "losses." Mechanical energy converted to heat energy. When we speak of a machine having an efficienoy of 50^ do we imply that 50% of the energy has gone out of existence ? Can we say in general that: Mechanical energy input = Mechanical energy output + amount converted to other forms of energy. HEAT ENERGY Why has it been customary to measure heat energy in units different from those used for mechanioal energy? Can we isolate a quantity of heat energy? The distinction between quantity of heat and temperature. Tempe rature . Do we have any basis for considering the temperature of a substance as fundamentally associated with the average kinetic energy of the molecules of the material? We shall study this question further in a later section. What types of physical phenomena are suitable for measuring temperature? Is the expansion of a substance like meroury necessarily the most accurate basis for thermometry? How do the centigrade and Fahrenheit scales differ? Why use the "ice" and "steam" points as the "fixed" points for a temperature scale? How can we convert temperature readings from centigrade to Fahrenheit, or vice versa? Why is the absolute, or Kelvin, temperature scale so important? Heat Energy Units. How do we use the calorie, or British Thermal Unit (BTU), in the measurement of heat energy? Is it logical to use the amount of heat necessary to raise 1 gm of HjO, I o C as a unit? What is the corresponding unit in the English system?

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C. CONTINUED Calorimetry. A p p l i c a t i o n o f Conservation o f Energy v o l v i n g only two s y s t e m s . Loss o f heat by one system = g a i n B a s i c law o f heat change, where t h e r e Change i n heat energy = ( S p e c i f i c = SW ΔΤ

t o heat t r a n s f e r s ,

in-

i n h e a t o f o t h e r system. i s no change o f s t a t e . heat)x(Wt)x(temp.change)

Mechanical E q u i v a l e n t o f H e a t . Why were t h e experiments o f Rumford and J o u l e which disproved t h e c a l o r i c t h e o r y o f heat and proved t h a t a d e f i n i t e amount o f mechanical energy was e q u i v a l e n t t o a d e f i n i t e amount o f heat energy so important? Mechanical e q u i v a l e n t : 4 2 , 7 0 0 gm.cm = 1 c a l o r i e o r 778 f t . l b = 1 BTU What p r o c e s s e s do we lcnow which i n v o l v e o r depend on t r a n s f e r s o f mechanical energy t o h e a t e n e r g y , or v i c e v e r s a ? What about heat e n g i n e s ? CHEMICAL ENER3Y Do chemical r e a c t i o n s always involve changes i n energy? What happens t o t h e energy ( u s u a l l y h e a t ) absorbed or l i b e r a t e d i n chemical r e a c t i o n s ? The chemist uses t h e terms exothermic and endothermlc t o d e s i g n a t e r a c t i o n s which l i b e r a t e o r absorb e n e r g y . How i s Conservation o f Energy o p e r a t i n g i n t h e c a s e o f c o n v e r s i o n o f energy l i b e r a t e d in combustion o f c o a l , g a s , or g a s o l i n e i n t o o t h e r forms o f energy? Do we u t i l i z e t h e energy o f o t h e r chemical r e a c t i o n s on a l a r g e s c a l e , e i t h e r d i r e c t l y o r by t r a n s f e r t o some o t h e r form? These q u e s t i o n s w i l l be considered much f u r t h e r next semester i n S c i e n c e A2. WAVE ENERGY What c h a r a c t e r i s t i c s have t h e v a r i o u s t y p e s o f wave e n e r g y , such as water waves, sound waves, and l i g h t waves i n common? Do a l l waves r e q u i r e a p h y s i c a l medium f o r t h e t r a n s m i s s i o n o f energy? Considering sound energy as t h e t r a n s m i s s i o n o f mechanical e n e r g y impulses from molecule t o m o l e c u l e , why should one e x p e c t sound t o t r a v e l slower (1100 f t / s e c , 3 3 0 m e t e r s / s e c ) t h a n l i g h t energy ( 1 8 6 , 0 0 0 m i l e s / s e c o r 3 χ I O 1 0 cm/sec)? Why do we o o n s i d e r sound waves as l o n g i t u d i n a l and l i g h t waves transverse? In what ways a r e t h e t e r m s : Frequency - n o . complete v i b r a t i o n s or c y c l e s per sec Period - time f o r one complete v i b r a t i o n o r c y c l e Amplitude ·. displacement from e q u i l i b r i u m p o s i t i o n Wavelength - d i s t a n c e between p o i n t s i n same phase on two s u c c e s s i v e waves used t o d e s c r i b e wave motion?

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C. COMTIfflJED If the fundamental relation governing all wave motion is that: velocity of propagation = frequency χ wave length what is the wave length of the radio wave from WEAF if the frequency is 660 kilocycles? Under what conditions do we find that the intensity of wave energy (i.e., the energy falling normally on 1 cm of surface) is inversely proportional to the square of the distance from the source?

Are the ears and eyes good instruments with which to measure sound and light energy? Where are they most in error, in estimating intensity or frequency? Wave Energy Conversion. What devices transfer wave energy to other forms or vice versa? Consider the chain of energy conversions involved in the detection of the light energy from the projection lamp by a thermopile, amplifier, and galvanometer. IN THE LABORATORY How oan we measure a quantity of heat energy?

SW Δ Τ

Meohanioal Equivalent of Heat. Using the apparatus supplied, study the conversion of mechanical energy into heat energy. Determine the mechanical equivalent of heat, through the measurement of the work done in gm.cm (force χ distance), and the heat energy transferred, as measured by the temperature rise of water and the known weight of metal parts of the calorimeter. What factors account for the difference between the results obtained, and the accepted values for this relation between gm.cm and calories? Energy Content of Illuminating GaB. Study the measurement of the heat energy content of the illuminating gas supplied by the gas company, with the Junker type calorimeter. Note that it makes use of the same principles as the mechanical equivalent of heat apparatus, measurement of the temperature rise of a known quantity of water, caused by a known amount of gas. The fuel value is usually given in BTU per ft3. Efficiency of a Gas Burner. Assuming that a good gas burner delivers heat energy at a constant rate, measure the rate at which the burner heats up a measured supply of water. By measuring the amount of gas used, and knowing the fuel value of the gas, determine the efficiency of a number of types of gas burner. Temperature Measurement. Study the measurement of temperature with a thermocouple. Calibrate it using the steam, ice, and liquid air points (-180°C). Use it to measure the temperature of solid CO,, (dry ioe). Assuming that the temperature at which it just glows red is about 500°C, by extrapola-

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tion, observe the approximate temperature in parts of the gas flame. Would all thermocouples give the stime calibration? What if two wires of the same kind were used? FOR STUDY AND READING ESSENTIAL Lemon, pp. 74-83, 116-119, 135-141, 333-346. Or Loeb and Adams, pp. 170-178, 207-217, 223-228, 230-235. Or Knowlton, pp. 107-118, 245-256, 265-274, 320-338, 369-378. SUGGESTED Chase, "Men and Machines." Kaempffert, "History of American Inventions." Knowlton, on Utilization of Energy, pp. 230-238, 257-265, 275-288. Lemon, pp. 372-384. Lenard, "Great Men of Science" on Helmholtz. Loeb and Adame, pp. 235-245. Miller, "Scienoe of Musical Sounds." Richtmeyer, pp. 53-56 on Rumford and Joule.

Sixth SECTION I I I

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ENERGY

(Continued)

C. CONSERVATION OF ENERGY (Continued) ELECTRICAL ENERGY Why not measure e l e c t r i c a l energy i n t h e same way we measure mec h a n i c a l energy? Measurement o f E l e o t r i c a l Energy. The Three Fundamental Concepts. Potential difference. S u p p l i e s t h e e l e c t r i o a l f i e l d which d r i v e s t h e negat i v e e l e c t r o n s along t h e c o n d u c t o r . U s u a l l y measured i n v o l t s - V. Resistance. A term used t o cover t h e o p p o s i t i o n t o the flow o f e l e c t r o n s along t h e c o n d u c t o r , analogous t o f r i c tion, U s u a l l y measured i n ohms - R. Current. The r a t e o f flow o f t h e e l e c t r o n s along the conductor - determined by t h e a p p l i e d p o t e n t i a l d i f f e r e n c e ( v o l t s ) , and t h e r e s i s t a n c e (ohms). Determined by n e , t h e net number o f e l e c t r o n s which pass a given c r o s s - s e o t i o n per second, m u l t i p l i e d by t h e charge on an e l e c t r o n . U s u a l l y measured i n amperes - I . Ohm's Law.

V R = —

A c o n s t a n t f o r a given c o n d u c t o r .

I s i t r e a s o n a b l e t o e x p e c t t h a t t h e r a t i o o f the v o l t a g e t o c u r r e n t should be c o n s t a n t over a wide range o f values? Ammeters and V o l t m e t e r s . The f o r c e on a conductor c a r r y i n g c u r r e n t i n a magnetic f i e l d i s p r o p o r t i o n a l t o t h e c u r r e n t and at r i g h t angles both t o t h e d i r e c t i o n o f t h e f i e l d and t o the d i r e c t i o n of the current. How do we use t h i s f o r c e t o measure c u r r e n t i n a simple galvanometer? Why i s t h e usual p r a c t i c e t o provide ammeters with a low r e s i s t a n c e i n shunt, and v o l t m e t e r s with a high r e s i s tance in series? E l e c t r i c a l Power. The w a t t . VI = V */R = I l R . The r a t e o f u t i l i z i n g e n e r g y . One watt i s e q u i v a l e n t t o about . 7 3 3 f t . l b , per second, or about 1 0 , 2 0 0 gm.cm per second. E l e c t r i c a l Energy. The product o f p . d . , c u r r e n t and time i n t e r v a l V i t , or ( V ' / R ) t . W a t t - s e c o n d s , or more g e n e r a l l y , k i l o w a t t - h o u r s .

IfRt,

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C. CONTINUED Equivalent to ft.lbs., or gm.cm. Which units appear on your monthly bill from the electric company? Direct and Alternating Current, DC. and AC. DCs constant voltage and current. AC: continually reversing voltage and current, sine wave form. What is meant by 60 cycle ACÎ Why must the peak value of 120 volt AC be larger than 120 volts, i.e., V 2 (120) or about 170 volts? Transformations of Electrical Energy. The "eleotrical age." The conversions of electrical energy to other forms are in general highly efficient, and are used most widely of all types of energy conversions. 1 kilowatt-hour = about 2,640,000 ft.lb = about 900,000 calories Transformations into heat and light The heat developed in a resistance = .24 I*Rt calories. How much of the energy supplied to a hot lamp filament is converted to visible lightî Batteries - sources of EMF. Dry oells - storage batteries. The generator. Transfer of mechanioal to electrical energy. Electrical and magnetic fields. The magnetic field produced by the current flowing through a wire. The eleotromagnet, increased field strength due to the iron core. Induced E.M.F.'s. Faraday's discovery in 1830 of the voltage induced in a wire moved through a magnetio field. The essential parts of a generator. The magnetic field: Field coils - iron frame. The armature: Coils of wire rotating in the magnetic field, in which voltage is induoed. Commutator and brushes: Reversing connections to armature coils at the proper moment so as to provide unidirectional flow of electrons in the external cirouit of a direct current (DC) generator. Or slip rings and brushes: Continuous connection to armature coils so as to produce alternating voltage; AC generator. And of course, a source of mechanical energy, steam, water power, etc. to rotate the armature. What determines how much mechanioal energy must be supplied to rotate the armature7 Is electrical energy "produced"? The motor. Transfer of electrical to mechanical energy.

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C. CONTINUED Based on the companion effect to that of the generator, i.e., the force exerted on a wire carrying current in a magnetic field. How does the motor differ from the galvanometer? The essential parts of a DC motor. The magnetic fields Field coils - iron frame. The armature« Coils free to rotate in the magnetic field due to the force exerted on them when current flows through them. Commutator and brushes: To reverse the current through the armature at the proper moment so as to provide continuous rotation in the same direction. And of oourse, a source of eleotrioal energy. Counter E.M.F. Why can a DC motor serve as a generator if its armature is rotated? Distribution of Electrical Energy. Long-distance transmission: The neoessity for high voltage, low current transmission to reduce I*R power losses in the resistance of the lines. The alternating current step-up and step-down transformer. Makes possible transmission of high voltage, low current over long distances, and stepping down to low voltage, high current for use in local distribution systems. Why can't we use transformers on direct current? Utilization of Electrical Energy. Energy conversions: Follow the energy changes from the sun's energy, to prehistoric plants of the Carboniferous era, to coal under a boiler, to the distribution of electrical energy to light cities, drive trains, and run industrial establishments. Large-soale energy projeets. Why do these huge plans, suoh as the TVA development, or the Boulder Dam projeot, always involve electrical energy? Is "cheap power" a possibility? Why does elractrical energy appear to be so fundamental? Is the distinction between electrical energy and the other forms of energy real? Does the electrical nature of matter foreshadow future developments? Is it possible to "store up" enerçy? On a small scale; on a large scale? Or for a short time; for a long time? IN THE LABORATORY Examine the various forms of galvanometers, ammeters, and voltmeters, to learn as much as possible about the purpose and prlnoiple involved.

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Note the contrast between the old instruments of the moving-magnet, fixed-coil type, and the modern instruments of the moving-coil, fixed-magnet, or D'Arsonval type. On what factors does the sensitivity of the suspension type galvanometer depend? What sets a limit to the obtainable sensitivity? Study the various ammeters and voltmeters, and draw typioal diagrams of the two types, with appropriate resistances in series or parallel. With suitable ammeters and voltmeters, measure the potential difference (volts) between the terminals of various types of eleotrio lamps, and the corresponding ourrents. Measure simultaneously, by means of an iIluminómeter of the photometer or photo-oell type, the illumination in candle power of the various types of lasçe. Calculate the re s i stance of the lamp filaments when hot, and the energy in watt-seoonds or K.W.H. supplied per hour of servioe. Compare the illumination produced per watt by the various types of lamps (i.e., the relative efficiency). How is the high effioienoy of the "photo-flood" lamps obtained? Measure the electrical energy, Vit (watt-seoonds), supplind to a direct current motor, and at the same time measure the mechanical energy, Fd (gm.cm), turned out by the motor, at various loads. If one watt-seoond is equivalent to about 10,200 gm.cm, how does the motor efficiency vary with the loads used? What happened to the "lost" energy? Using an eleotrioal calorimeter, measure the quantity of heat energy in calories developed by a definite amount of eleotrioal energy (wattseoonds). What is the relation between the units used to measure the two forms of energy? FOR STUDY AND READING ESSENTIAL Lemon, pp. 222-262, 265-268. Or Knowlton, pp. 320-339, 369-379, 379-390. Or Loeb and Adams, pp. 324-328, 333, 373-379, 383-390. SUGGESTED Hodgine and Magoun, "Behemoth." Knowlton, on Utilization of Energy, pp. 230-239. Loeb and Adams, on Heat Death, pp. 235-245. Pupin, "From Immigrant to Inventor." Richtmeyer, on Faraday, pp. 60-70. Saunders, on Generators and Motors, pp. 400-410.

Seventh week SECTION III - ENERGY (Continued) C. CONSERVATION OF ENERGY (Continued) Conservation of Energy and Transformations of Energy. How has man's u t i l i z a t i o n of energy progressed since the beginning of time? Why has the increase in the use of energy gone further since 1900 than in a l l the preceding centuries? What further e f f e c t s on s o c i a l and p o l i t i o a l systems oan we expect i f the u t i l i z a t i o n of energy continues t o inoreaee at i t s present rate? Viewed in the l i g h t of your study of various phenomena as outlined i n previous sections, how fundamental t o modern c i v i l i z a t i o n are these f a c t s about energy? Do you expect energy t o beooaie more important or less important in the future than i t i s at present? Can any appreciable f r a c t i o n of our human a c t i v i t i e s be independent of these phenomena based on or u t i l i z i n g energy? Broader aspects of the conservation p r i n c i p l e . Is i t basic in a l l phenomena, or does i t break down? Are we f r e e from the perpetual motion idea? The F i r s t and Second Laws of Thermodynamics. A v a i l a b i l i t y of Energy. How can we have energy, and yet not have i t a v a i l a b l e ? Is the a v a i l a b l e energy of our earth decreasing continually? How abouh. our coal, gas, o i l , e t c . ? W i l l we eventua l l y use up our supply? Is the universe as a whole running down? W i l l we eventually s u f f e r "heat death"? D. THE PARTICLE NATURE OF MATTER With the background gained from our studies of energy, l e t us look baci-: over our e a r l y considerations of the nature of matter and enlarge our understanding of the atom, as a basis f o r the k i n s t i c theory of matter, and the r e l a t i o n between matter and energy. Early Speculation. What did Democritus and other e a r l y thinkers r e a l l y know? How did the f i r s t experimental evidence grow out o f the work of Dalton, Boyle, and Avogadro on the nature of gases? Further Development of Atomic Hypotheses. Atomic Structure. The hard spherical atom. Why did the concept of the atom as an i n d i v i s i b l e , hard, spherical, elementary p a r t i c l e o f the element p e r s i s t so long? Was t h i s concept s u f f i c i e n t f o r most of the e a r l y work oil gases, l i q u i d s , s o l i d s , and chemioal reactions?

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. CONTINUED Ideas about internal etruoture. How did the idea of a definite internal structure for the various atoms begin to grow out of the early experiments of Geissler, Hittorf, and Crookes on electrical discharge in gases, culminating in the discovery of the electron by Sir J . J . Thomson in 1897? Atom models. Why does the scientist attempt to build a model? When should we be satisfied with a model? To what fraction of us do our models represont absolute reality? Have atomic hypotheses helped or hindered discoveries? Early atom models. The Thompson atom. Positive charge distributed throughout the atom. Displaced by the Rutherford nuclear atom. The Lewie-Langmuir atom. A statio geometrical structure, useful for some chemical interpretations but now largely discarded. Rutherford-Bohr nuclear atom model. The nucleus. How did the experiments of Rutherford, firing alpha particles (helium nuclei) at various atoms establish the idea of a tiny, positively chargod central nucleus, containing most of the mass of the atom? The internal structure of this complex "central sun," having a range of radius of about, 2-8 χ 10~13 o m from hydrogen to uranium, now appears to consist of protons (hydrogen nuclei, approximately 1.007 mass units, one + charge), and neutrons (approximately same mass as proton, but no electrical charge). The external "planetary" eleotrons. Mass about 1/1840 that of proton, one - charge. Equal in number to the protons in the nucleus, since the atom is electrically neutral. Early ideas on electron "orbits," electron "shells, A dynamic atom. Necessary to produce a stablo atom, with the negative electrons in equilibrium under the electrical attraction inward to the positive nucleus, and the centrifugal force outward. These ideas, together with the modifications of Bohr, and others we shall consider further in the section on Radiation. Periodic Relations among the Elements. Complex Atoms. Development from the simple -.Hi atom with one proton and one electron, to the more complex atoms up to the uranium atom, tj238i with a nucleus of 92 protons, and 146 neutrons, and I external "planetary" electrons grouped in several "shells.

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D. CONTINOED At orni o Weight. The weight o f the atom in mass u n i t e based on 0 1 6 as 1 6 . 0 0 0 0 . Why does the atomi o weight depend almost e n t i r e l y on the nuoleüs? Atomic weights of t h e various atoms are nearly whole numbers. Atomio Number. The charge on the nuoleus, i . e . , the number o f nuclear protons, or e x t e r n a l e l e o t r o n s . Isotopes. The e a r l y experiments. The work o f Aston, Dempster, Urey, and o t h e r s . P r a o t i o a l l y a l l elements are f a m i l i e s o f atoms, having: Nearly the same physioal and oheinioal p r o p e r t i e s . The same atomio number, i . e . , same number o f protons i n nuoleus, and same number o f e x t e r n a l e l e o t r o n s , and a l most iderrtioal extr&nuclear s t r u o t u r e ; But < Contain d i f f e r e n t numbers o f neutrons i n the nucleus, t h e r e f o r e have d i f f e r e n t atomio w e i g h t s . For example, we have : pu 204 p. 205 206 207 208 209 82 ' 82 ' 82 ' 82 '82^ '82^ and a l s o other isotopes in very small q u a n t i t i e s . Observe the notation whioh i n d i c a t e s both atomic number and atomic weight. Hydrogen and deuterium - Urey and

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Heavy water D t 0 Chemical Atomio Weights. The average o f t h e weights o f the mixture of isotopes or a given element. Ordinary lead averages about 207.22 f o r example. Mende l e J e f f ' s Periodio T a b l e . Are t h e r e others? A large number o f physioal and chemical p r o p e r t i e s , such as d e n s i t y , atomio s p e c t r a , b o i l i n g p o i n t , ohemioal v a l e n c e , e t o . vary p e r i o d i o a l l y among the elements. Have our ideas of the periodio nature o f the elements progressed sinoe Mendelejeff 7 E . THE KINETIC THEORY OF MATTER How o e r t a i n i s our experimental b a s i s for the b e l i e f t h a t the molecules o f a l l matter are i n rapid and continual motion, and t h a t temperature i s simply a measure o f the average k i n e t i c energy, l/2(W/g)v , o f the moleoules? How oan we measure thé e f f e c t o f a large number o f moleoules i f we cannot know what i s happening t o every one o f them at a p a r t i c u l a r time? Why are our experimental and t h e o r e t i o a l studies o f matter i n general onlv «-feft-ti s t ì rtftl ?

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E. CONTINUED Gases. Characterized by Very Small Interatomio F o r c e s . The atoms make frequent e l a s t i c impacts with each o t h e r , much l i k e e l a s t i o b a l l s , but are i n contact with t h e i r neighbors only a email f r a c t i o n o f the t o t a l t i m e . Brownian Movement. How does the continual j e r k y motion o f microscopic pollen g r a i n s , f i r s t observed by Brown, show t h e behavior o f the molecules b u f f e t i n g them about? Do we see the moleoules themselves? Development o f Ideas About Gas P r e s s u r e . Pressure = Force/area = force per unit area ( i n gm/cm*, or lb/in*, eto.) How did J o u l e ' s work on the Meohanioal Equivalent of Heat lead t o his idea t h a t gas pressure was due t o the constant bombardment o f the walls o f a container by the gas molecules? Can we prove experimentally t h a t the r e l a t i o n between gas p r e s sure and the average k i n e t i c energy o f the molecules i s such that χ « Ρ = -j , where w = weight/cm' or d e n s i t y . The v e l o c i t y o f the average a i r moleoule (Nf or 0 , ) at ordinary temperatures i s about 1600 f t / s e c . All types of molecules of whatever weight have the same average k i n e t i o energy l / 2 ( w / g ) v * , at the same temperature. How much f a s t e r does a hydrogen molecule Hp t r a v e l than an oxygen molecule 0 t , in order t h a t the k i n e t i o energy s h a l l be the same? IN THE LABORATORY Measurement o f P r e s s u r e . I n v e s t i g a t e the p r i n c i p l e involved i n forms o f pressure measuring devices manometers, Bourdon gauges, meroury airplane a l t i m e t e r s , airplane speed

the operation of the various a v a i l a b l e , suoh as mercury and aneroid types o f barometers, indicators, e t c .

Measurement o f Barometrlo P r e s s u r e . Why does the barometer measure the weight of the a i r above i t ? Read the barometer i n the l a b o r a t o r y , on the 1 s t and top f l o o r s . Are the readings c o n s i s t e n t ? Can we compute the v e r t i o a l distanoe between the barometers? What do you know about barometric pressure, as used i n weather maps, and weather f o r e c a s t i n g ? Brownian Movement. Study, vrnder proper i l l u m i n a t i o n , with a high power microscope, the motion o f 1 Smoke p a r t i c l e s in a i r . 2 Gold p a r t i c l e s in w a t e r . What types o f path do the p a r t i c l e s buffeted about by the high speed molecules t r a v e l ?

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How good i s t h i s as a foundation f o r the k i n e t i o theory? Would you expect the wing of an airplane t o show a large Brownian movement? Boyle's Law. I f s u f f i c i e n t time i s a v a i l a b l e , determine how acourately Boyle's law, PlV x = P2V2» enables you t o compute the volume of a i r in a tank under pressure. Observe by pumping a i r into a s t e e l tank of known volume t o a high pressure, and then measuring the volume of a i r at atmospheric pressure by allowing the a i r to escape through a gas meter. FOR STUDY AND READING ESSENTIAL Bazzoni, "Energy and Matter," pp. 18-48. And Loeb and Adams, pp. 219-223, 260-267, 283-286. Or Lemon, pp. 95-105, 149-157, 308-315, 325-330. SUGGESTED Bazzoni, "Energy and Matter," pp. 1 - 1 8 . Knowlton, pp. 143-155. Lenard, "Great Men of Science" on Boyle, Watt, Dalton, J o u l e , Clausius, and Kelvin, Loob and Adams, pp. 272-274, 286-288, 290.

Eighth Week SECTION III - ENERGY

(Continued)

E. THE KIHETIC THEORY OF MATTER (Continued) Gases (Continued) How have our ideas developed from the work of Dalton on the partial pressures exerted by mixtures of gases, the compression of gases by Boyle, the ideas of Avogadro, and on up to the refined theories of Clausius, Maxwell, and others, viewing gases from a s t a t i s t i c a l mechanical point of view? Avogadro's Hypothesis. A l l gases under the same oonditions oontain equal numbers of molecules. Boyle's Law. The product of pressure and volume, ( i f temp, is constant), 1 W ν* PiV t =P f V t = a constant = — ύ

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How well do gases follow this lawî Are there any assumptions involved in Boyle's law that are not quite correct? Temperature. The molecules of a l l gases have the same average kinetic energy, 1 / 2 (w/g) ν * , at the same temperatures. The average v e l o c i t y of an 0 t molecule in air is about 1600 ft/sec under ordinary conditions. The H, molecule weighs i/le as much as the 0, molecule. The average v e l o c i t y of an H t molecule is therefore λ/16 or 4 times that of the 0 , moleoule, about 6400 f t / s e c . Absolute zero. The pressure of an ideal gas approaches zero linearly at about -273.1°C as the temperature is lowered, volume being kept constant. The volume behaves in the same way, i f pressure i s kept constant. That i s , molecular kinetic energy, l/2(w/g)v* approaches zero at that temperature. Absolute, Kelvin or Thermodynamic scale of temperature. Using -273.1°C as the zero point of a new scale, the pressure and volume of an ideal gas become linear functions of T. I f the volume i s held constant: 1 D ν* Ρ = — is proportional to Τ 3 6 Ρ Τ or = ττ1 Charles or Gay-Lussac's law fg 12 I f pressure is held constant; V i s proportional to Τ

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CONTINUED General gas law. Using these relations, and Boyle's law: PV = RT =

_1__W_ ν * 3 g

R = General gas constant = 84,800 cm/de g. C

or The last two expressions are useful when the weight of gas changes. Note that absolute and not gauge pressure must be used, and that likewise absolute and not centigrade temperatures must be used. Bow do we use these relations in aotual problems? What are the limitations of the general gas law? Kinetio Theory Concepts. Are all the moleoules of a gas moving alike? Mean Free Path. The average distance a moleoule travels before it makes a oollision with another molecule. Usually: 1 Ν = no .mol/cm* M.F.P.