"Mr.Watson, come here I want to see you", were the first words transmitted on a telephone line by Graham Bell on March 1o, 1876. So what is a Telephone? Telephone or Phone as we call it is a device that converts sound into electric signals and transmitted over long distances which are converted back to sound at the receiver's end. There were about 6 billion subscribers worldwide in 2009.
Telephone is a communication device but there was a lot of miscommunication on the invention of the phone. Who exactly invented the phone is a little fuzzy. A lot of scientists were individually working on the concept of telephone when Graham Bell came up with the device and transmitted his first message on March10,1876. He beat another scientist Elisha Grey only by a few hours when he filed for the patent. Bu the didn't have a working phone when he applied for the patent. Only three weeks later did he build one.
The first concept of a telephone was first mentioned by Francis Bacon in 1627. But it was around the 1830's when the idea of transmitting sound as electrical waves started gaining momentum. One of the first pioneers in this field was Stephen Gray, a chemist who transmitted electricity over 300 ft wire . Later on a couple of Dutchmen developed a jar called the Leyden Jar to store static electricity but could not use the charge really for anything. it was too small an amount. There were a few other things like magnetism and the battery, that had to be understood and invented before the telephone research evolved. It was only after the Battey got invented, the research on telephone moved forward.
In 1820 a Danish physicist did an experiment where he made the compass needle move north when he placed it under an electric wire. Michael Faraday in 1821 did the reverse of this which he termed "Electric Induction". He generated a weak electric current to flow in w ire rotating around a permanent magnet. The result that mechanical energy could be converted to electrical current.
The simplest way to understand this is take two cups and pass a string between them. As long as the string is straight and really tight this should work. Now when one person talks into the cup the other person will be able hear the other person talk. When the person talks the bottom of the cup vibrates with the sound waves and these are passed through the string to the other cup which vibrates at the same speed as the originating cup producing sound waves. In the older phones, the person speaking vibrates a metal diaphragm.The diaphragm's vibrations in turn compress and uncompress carbon granules, changing their resistance. The current passing through changes based on the compressions of the granules.At the receiver's end, the changing current runs through a speaker and causes the diaphragm to vibrate, so the second person hears the first person speaking. The electrical transmitter a thin plastic sheet is painted with a metallic coating.The plastic separates the coating from another metallic electrode and maintains an electric field between them which produces small variations in voltage.The voltage is amplified to transmit over the telephone line.
A phone takes very little power to operate, as little as 6-12 volts and about 30 amps. A pair of copper wires for each phone are buried deep when the telephone company puts in a new connection so that no storms cut them off.
The phone company has extensive backup power supply which will supply current even when there is a power outage and so we continue to receive phone calls during a power outage too.