The Telephone - how it works? - CBT

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A CST PUBLICATION

HOW IT WORKS

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1875 The first telephone instrument made by Alexander Graham Bell in 1875 I

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1880

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This device required the user to speak into the box with the receiver to his ear (1880)

An Edison receiver (1879) I

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1880 ....

The Gower-Bell telephone of the early 1880's with two listening tubes

1905 The telephone ttoday

The candlestick telephone of 1905 I

R. Watson, come here, I want to see you," shouted an angry Bell. Watson jumped out of his chair. There was no one in the room. Yet he'd heard a voice. It was a familiar voice and it was loud and clear. Then suddenly it hit him. The telephone. It had come alive at last. The miracle had happened. . Watson rushed to Bell's room, breathless with joy. "I could hear you. It works," he said. That was March 10, 1876. More than a hundred years ago. From ship to shore; from air to land; from car to car; from just about anywhere to anywhere today you can speak to someone by just dialling a number. In fact, you have the world at your finger-tips. And when Astronaut Rakesh Sharma calls up Mrs. Indira Gandhi from space you just take it in your stride. So dramatic has been the development of the telephone. And only forty years before the telephone was invented, man was patting

himself on his back for having perfected the methods of communication. That was when the electric telegraph was used. It was in 1838 that the American, Samuel Morse, patented his single wire telegraph. His design used the famous Morse code in which combinations of short and long signals - dots and dashes - indicate letters. Messages were sent at up to ten words a minute with a hand-operated key and were received as marks made by a pen on a paper tape. These signals had to be decoded and written out by hand. In 1855 Professor David Hughes invented a printing telegraph. The operator sent messages from a keyboard, each key of which represented a letter. The machine turned the letters into electric signals automatically and, at the other end, another machine printed the message. These were major breakthroughs in the field of communication, but still not the same as 'talking' to someone, and nowhere near having a cosy chat with someone.

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It was at this time that Alexander Graham Bell, the young professor of speech, began his experiments with electricity. Often he would visit the mills and factories located near his house and observe how the machines were operated. Once he called on Charles Wheatstone, the inventor of the . magnetic needle telegraph. So impressed was he by this mail that he determined to follow in his footsteps. Bell was keen to develop a telegraph· system that would allow multiple transmission of messages at once. He felt that this could be achieved by transmitting each message on a separate, specially tuned steel strip, or reed. Each reed would vibrate a different number of times per second and so produce a different musical note. It was while one such experiment was being carried out, on June 2, 1875, that a receiving reed, which was being watched

closely by his assistant, Thomas Watson, in another room, failed to vibrate. Watson thought the reed was stuck and pulled at it. When he did that. a similar receiving reed vibrated in Bell's room. "What's this!" said Bell astonished, but realized almost immediately that he had hit upon something great. He had discovered that a tiny electric current caused by one vibrating reed was powerful enough to cause another reed to vibrate audibly. He also realized that instead of a single note the reed had reproduced several notes. Human speech, as Bell knew only too well, is also made up of a mixture of sounds of different frequencies and Bell believed that he could use this system to transmit the human voice. Lo and behold, a month later, Bell produced a pair of simple telephones. Bell had made a deep study on sounds as he had always wanted to help deaf and dumb children. He, therefore, knew that a stretched membrane would be more suitable for sound

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. Bell demonstrating the first telephone

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reproduction than a reed. He finally decided to use an iron diaphragm. On March 10, 1876, when he accidently discovered that his phone worked, he was delirious with joy. It was the first time in the world that people could talk to each other over long distances and feel that they had almost met the person. After all there can be no substitute for a human voice. Bell was keen to promote the idea of this new device and travelled extensively in the United States and Europe to spread the word. He even demonstrated how one could talk to someone under water. But most people pooh-poohed the idea. In London, a post office official said it would never catch on because there were sufficient messenger boys. Finally on January 24, 1878, Bell carried out a demonstration for Queen Victoria at Osborne House, on the Isle of Wight. So impressed was the Queen that she asked Bell to supply her with telephones Immediately.

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As news spread, a keener interest was created in the telephone, though it was restricted to small areas until the 1890's. Individual subscribers were connected to each other by exchanges that were controlled by operators. When somebody wished to make a call all he did was lift the receiver and wait for the operator's response. "Number, please," the operator would say and connect you to the number you wanted. In fact, so personal was everything those days that on some exchanges all you did

An 1879 hand-operated switchboard

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was lift the receiver and ask for the person you wished to talk to. Only one had to shout in order to be understood by the other person. Early models resembled a box camera with a round projection at one end. This served as the transmitter and receiver. So anyone making a call had to be extremely careful while moving his ear and mouth. Bruised lips and ears were not an uncommon sight. In fact, one model carried the notice: "Do not listen with your mouth and talk with your ear!"

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As Bell's transmitters had poor sensitivity, calls were limited to a few miles. It was at this time that Thomas Alva Edison, the famous American inventor, stepped in. Edison was the next best thing that happened to the telephone. He produced a telephone with a separate mouthpiece and a much superior transmitter with a carbon component. When spoken into,it changed the sound of the voice into a varying electrical signal which was converted back into speech by the ear-piece at the other end. By the beginning of the 1900's, the telephone had grown in popularity, especially in the United States. Some exchanges were so large that there were long lines of operators seated at switch boards made up of hundreds of plugs and sockets.

India, believe it or not, was one of the first countries in the world to have a telephone exchange. And Calcutta was where it all started. In 1881, barely five years after Bell made his discovery, a 50-line exchange was set up in Calcutta. Then came the automatic telephone exchange with 700 lines, which was established in Shimla in 1913. But it was only after 1951 that the Indian telephone service made rapid progress. Subscriber Trunk Dialling (STD), first introduced between Kanpur and Lucknow in 1960, now operates on practically every route in India and many outside the country too.

'Tele' literally means 'at a distance' and 'phone' is an instrument using sound. Thus 'telephone' would imply 'an instrument that carries sound from a distance.'

Today telephone users in most parts of the world can dial 80% of the world's subscribers directly. Telephone 'hot-lines' keep world leaders in contact with each other to avoid the accidental outbreak of a nuclear war. Even on the battlefield it is now possible to link soldiers to the international telephone network and a person from the most isolated oil platform in the sea can make calls throughout the world. Your parents can hold international business meetings by merely going to a closed circuit television studio and talking to executives in similar studios in other countries while the television pictures and the sound are being carried over the telephone network. The telephone network has also been able to link computers in many countries to vast information networks. It can transmit television programmes such as the Olympic Games to more than a 100 countries. It can

be used to turn a television set into a terminal connected to a computer, providing vast amounts of information through videotex. In the future this could form the basis of an electronic mail service with people sending private messages from one television set to another via the telephone network. It would be cheaper and much faster than conventional post. With so much happening around us it is hard to believe that once upon a time messages were sent by using a line of bonfires on hill-tops, by beating drums or tying notes to carrier pigeons speci.ally trained to fly home quickly from a distance.

Few of us realize how complex and ingenious is the mechanism that is set in motion the moment one dials a telephone number. How does your voice get carried through miles and miles of wire? How is it that you can hear even kids crying in the background, doors slamming and music playing through the wires of the telephone?

Without the telephone today, business and social life would be seriously disrupted. This was demonstrated in 1979 when a strike by telephone workers halted the telephone system in Ireland for several weeks. Millions of pounds worth of orders were lost because companies could not reply quickly to requests and their business was won by competitors.

In order to understand this let's first understand sound. Air helps sound to travel. If there was no air we would not hear any sound. You can prove this by placing a bell under a glass bowl and ringing it. You'll be able to hear it clearly. Now if you draw the air out with a suction pump, the sound of the bell will disappear. This is because there is nothing to carry the sound. Air is something quite real, even though we cannot see it. Just as ripples are made in water, they are made in the air too and How sound travels

are called sound-waves. Let us take for instance, a sheet of metal and see what happens when we hit it. The force of the blow makes the metal tremble. The to and fro motion so caused is called vibration. A guitar string vibrates when we pluck it. As the metal sheet vibrates it pushes the air forward and backward quickly, so that little ripples or waves are made; which travel away from the metal in all directions. These waves in the air are so tiny that you cannot feel them, yet they are strong enough to make another sheet of metal vibrate when

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Smoke signals .•.. carner pigeons horses. man has used all these to fulfil a vital need-eommunlcatlon.. so rapId has been the progress that today. thanks to the telephone. we literally have the world at our fingertips

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