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Beverly Maldaner, age 9, of Lethbridge, Alberta, Canada, for her question:

HOW DOES A TELEPHONE WORK?

 

Back and forth across North America weaves an incredibly vast network of wires that carry messages between millions of telephones. While a great many local and long distance calls are carried by radio systems, most of the messages travel along copper wires. About 98 out of every 100 telephone wires are bound into cables with some containing more than 4,000 individual wires.

When you speak into a telephone's mouthpiece, the sound waves of your voice go into a transmitter. An electric current then carries the sound across the street or around the world to a telephone receiver.

Behind your phone's mouthpiece is a thin, round metal disk called a diaphragm which works much like a human eardrum. When you talk, your sound waves make the diaphragm vibrate. Depending on the variations in air pressure caused by the varying tones of your voice, the diaphragm vibrates at various speeds.

A small cup filled with grains of carbon is located behind your telephone's diaphragm. As the diaphragm presses against the carbon grains, low voltage electric current goes through them.

When you speak in a very loud voice, the sound waves press hard on the diaphragm and in turn the diaphragm presses the carbon grains tightly together. When the sound is soft on the telephone, the sound waves push lightly on the diaphragm and it in turn only puts a light pressure on the grains.

The pattern of the sound waves regulates the pressure on the diaphragm and it in turn regulates the pressure on the carbon grains. Depending on how tightly the grains are being pushed, the electric current becomes weaker or stronger as it goes out on the telephone wire.

Your telephone's receiver works much like human vocal cords. Two magnets located at the edge of a diaphragm causes it to vibrate. The action of the electric current passing through the electromagnet causes the diaphragm to vibrate according to the speaker's speech pattern. As the diaphragm moves in and out, air in front of it is pulled and pushed with the pressure setting up sound waves that are the same as the one sent into the transmitter. The sound waves go into the ear of the telephone listener and he hears the words of the speaker.

Automatic switching equipment can connect almost any two telephones anywhere on the continent. More than 99 percent of the telephones in North America are dial operated and switched automatically. As you turn numbers on your telephone dial, clicks are sent electronically to automatically controled centers were the connection between your telephone and the person's you are calling is completed.

Our phones have come a long way since Alexander Graham Bell's first one in 1876.

 

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