How Does My Voice Go over the Telephone?
A basic phone consists of a microphone (which you talk into), an apparatus to change your voice into electric signals, a means of sending the signals to their destination (say, your friend’s ear), and (on your friend’s end) a receiver which then changes the electric signals back into your voice (or an approximation thereof).
The key is something called “variable resistance.” When you speak into a telephone, the sound of your voice causes a thin metal plate inside the mouthpiece to vibrate back and forth. This plate, called a “diaphragm,” is part of an electrical circuit.
It changes the sound waves of your voice into electrical signals that travel over the telephone wire leading to another telephone, where someone is listening. There the electrical signals cause another diaphragm inside the receiver to vibrate.
The vibrating diaphragm makes sound waves similar to your voice — and so the listener hears what you are saying.