how it work the telephone

A CST PUBLICATION HOW IT WORKS THE .L J 1"" I I ~ , BY NAVKALA ROY DESIGNED AND ILLUSTRATED BY SUBIR ROY How it works . __ . THE CHANGING SHAPE OF SOUND I I- 1875 - The first telephone instrument made by Alexander Graham Bell in 1875 I 1879 1880 1880 1905 The telephone t- today I The candlestick telephone of 1905 The Gower-Bell telephone of the early 1880's with two listening tubes This device required the user to speak into the box with the receiver to his ear (1880) I An Edison receiver (1879) 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. o 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 '" . Bell demonstrating the first telephone I / Number, please 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 • . • • • • . . 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. • An 1879 hand-operated switchboard 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!" • • Do Not Li~ifN With YWR Mouth A~d 1ciJk with • OUI" Bo.Y'! • ~ 0 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 [...]... carbon and through the wires of the telephone flows an electric current The moment sound-waves hit the thin piece of metal it bends a little - so little that you cannot notice it When it bends (or vibrates) it squashes up the carbon The grains thus get tightly packed When there is no pressure on the diaphragm the grains are let loose again This too you would not be able to detect with the naked eye What... world, provided the same person speaks each time, because the Command Dialer is a one-man-machine and it will not respond to different voices This book, one of a series of information books, introduces the child to the marvels of the telephone -how it works and how it developed Others in this series include: • • • • • • The Television The Motor Car The Aeroplane The Clock The Ship The Railway Train... Electromagnet In the receiver of a telephone is a thin metal disc or diaphragm, just as in the mouthpiece But the receiver does not have the little container of carbon grains Instead there is an electro magnet, that is, a magnet worked by the electricity coming through the wires The more the electricity coming through, the more powerful the magnet becomes This magnet pulls on the thin metal disc in the receiver... through the two cups Knot it well so that it doesn't come out And that's it As long as the thread is stretched out tight, you have your telephone One person talks into one ice-cream cup the bottom of which functions as a diaphragm and the other person puts his ear to the other cup When you speak into the cup you make t~e b~ttom vibrate_ The thread carries the vibration by little tugs and makes the other... 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... diaphragm vibrate in exactly the same way That makes new waves of the same kind in the other cup and so the other person hears what you say You'll be able to hear each other as long as the thread is kept tight • • • • distance it would gradually reduce in strength and would not be strong enough to work the Wherever there are telephones there must be wires These wires are special as they have to pass over... sound A telephone works basically on the same principles - the carrier of the sound being electricity When you want to talk to a friend you lift the receiver and dial a number Your line is then connected to your friend's at the telephone exchange Electricity flows through the wires The sound-waves of your voice make the electric current stronger and weaker as the case may be In your friend's phone the. .. routed through several other exchanges All this is done in a matter of seconds and before you know it you are connected to the 1 Exchange 2 Satellite 3 Exchange 4 Earth '63' exchange and you can dial the rest of the numbers The switches that locate the other numbers are known as 'selectors' They move in two In some countnes the telephone system provides children with bedtime stories It takes a message for... To avoid this each telephone has its own set of wires running to a telephone exchange or central office When you pick up the receiver and dial the number you want, your phone is immediately connected to the exchange.lt is then that the next step of the journey is determined If you At the exchange 00 want to speak to someone in the neighbourhood, the switchboard at the exchange lets the current from your... start dialling Let's suppose that the number you want is 634520 The first two digits, that is '63' represent the exchange When you turn number 6 to the dial stop you are only winding up a spring in the dial mechanism The moment you let go, the dial returns under the tension of the spring and transmits six electrical 'kicks' along the line The number of 'kicks' correspond to the number dialled, o0 0 () Ie) . the wires of the telephone flows an electric current. The moment sound-waves hit the thin piece of metal it bends a little - so little that you cannot notice it. When it bends (or vibrates) it squashes. 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. 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