Joe Mauch, age 11, of Montery Park, CA, For his question:
How does a voice come over a telephone?
A telephone conversation is really a carbon copy of voices. The carbon is right there in the mouthpiece. It is a small box of carbon coal dust. The receiver of the telephone is an artificial ear. Between the mouthpiece and the receiver voices travel soundlessly over miles of electric wire.
The voices en route are soundless because they travel as electric impulses. Alexander Graham Bell figured out how to change the sounds of voices into pulses of electricity. He also figured out the artificial ear necessary to change the impulses back into sounds again.
The sound of your voice startles the air around you. Air molecules are set joggling and pile up into waves, Your speaking voice is a series of changers in pitch and volume. Its vibrations vary with every change. This stream of changing vibrations strikes a thin metal sheet called a diaphram in the telephone mouthpiece. The diaphram ,joggles forward and backward with the changing pitch and volume of your voice, It throbs in step with your voice.
Behind~ the diaphram is the small package of carbon grains. Both the diaphram and the box of carbon are loaded with electric current, The carbon varies the current in step with your voice. When the grains are packed close, they let through more current. When they are loosely separated, they let through less‑ current.
As you talk, the diaphram presses and relaxes onto the grains of carbon. They let through more or less current in time with each variation in your speech. This changing pattern oaf impulses passes along the copper wire. It is carried over the necessary miles as pulses of electricity.
Finally the carbon copy arrives at the artificial ear ‑ the hearing piece of the telephone set. This is where the electric impulses are changed bark again to sounds, This receiving set is actually a small electromagnet. From its coils comes a copy of the strong and weak electric impulses started by your voice.
The electromagnet works with an iron diaphragm. A strong impulse pulls the diaphragm inwards. A weaker impulse lets it relax. The iron diaphragm is vibrating. And vibrations make sounds. The sounds are a faithful copy of the electric impulses carried over the wires. The electric impulses are a faithful copy of your voice.