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Have you ever wondered how you can talk to a person on one phone and from another phone, the person can hear you?  What if the phone doesn’t have a cord?  Read on to find out this and more interesting information!

A telephone is a device that sends and receives voice messages, usually by electric current.  People can talk with each other at distances where a human voice cannot travel that far.  In just a few seconds, you can telephone a person across the street, in another country, or on another continent.

A dialing mechanism enables callers to enter telephone numbers to who they are calling.  It is built into the handset in between the earpiece and the mouthpiece, or it could be a part of a separate base unit, which is the device that holds your handset and is connected by a cord.  When these keys are pressed, each key generates a certain number of electronic pulses.  Computers in the telephone network direct the call from pulses and tones.

When the person calling speaks into the mouthpiece, the telephone changes the sound waves of the person’s voice into electric currents.  The variations in the electric current are therefore an electric "copy" of the speaker’s voice.  When a person speaks into the mouthpiece, sound waves hit the diaphragm.  The resulting vibrations change the distance between the diaphragm and the backplate and the strength of the electric field.  These variations in field strength trigger corresponding variations in an electric current.  The current variations are an electric "copy" of the speaker’s voice.

The receiver converts the electric current coming through the telephone line into a duplicate of the speaker’s voice.  The receiver is built into the handset, behind the earpiece.  In a receiver, an iron diaphragm in a flexible frame is surrounded by a ring-shaped permanent magnet.  The permanent magnet exerts a constant pull on the diaphragm.  Another magnet called an electromagnet is attached to the other side of the diaphragm.  This magnet is made up of metal with a coil of wire around it.  When the electric current flows through the coil, the electromagnet becomes magnetized.  The current moves in two directions.  When it moves in one direction, the resulting magnetism adds to the pull of the diaphragm more strongly.  When the current moves in the other direction, the resulting magnetism opposes that of the permanent magnet and reduces its pull on the diaphragm.  The variations in magnetic pull cause the diaphragm to vibrate.  It pulls and pushes the air in front of it, producing pressure changes that create sound waves almost the same as those of the speaker’s voice.  The sound waves strike the listener’s ear, and the listener hears a duplicate of the speaker’s voice.

In the 1950's experiments involving communication satellites demonstrated that a radio signal could be sent to a satellite thousands of miles out in space using a large earth station.  It was found possible to make a passive satellite system by using metalized balloons placed in orbit.  To talk to someone on the phone today, there doesn't always have to be a telephone line running between the phones.  Phone companies can also use radio signals and satellites to send voices over long distances.

Cellular phones work in a similar way.  They don't have cords, so they transmit voices through radio waves.  The radio waves from cell phones don't bounce off satellites.  They bounce off antennae put up by cellular phone companies.  Cell phones won't work if they are too far from the closest antennae just like cordless phones won't work if they are too far away from their bases.  This happens because the radio waves can't travel that far to reach the antennae.  A cordless phone sends radio waves to the base of the phone which then sends the waves through telephone wires the same way a regular telephone does.

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