When you call your friend on the phone, how does the sound of your voice reach them? You speak into the mouthpiece of your phone. The sound waves push on a thin sheet of metal called a diaphragm.
The diaphragm then vibrates. It presses against a small cup filled with carbon grains.
Electricity passes through the carbon on its way through the telephone wire. When the carbon grains are squeezed together, the electric current gets through easily. But when the grains are spread apart, only a little current gets through. So the vibrating diaphragm causes strong or weak pushes of electricity to travel through the telephone wire.
Your friend hears what you say through the earpiece on her phone. Inside it is an electromagnet a long coil of wire wound around an iron core. The strong or weak pushes of electricity reach the electromagnet. They cause it to make strong or weak pulls on another diaphragm. This diaphragm vibrates and makes sounds just like the ones your voice made. So your friend hears a copy of your voice-a copy made by electricity in a wire.
The first telephone was not like our phones today. You could speak into it but you could not hear the other person on it. Alexander Graham Bell first used it in March 1876. But by October of that year, Bell had the first two-way conversation on his invention.
Picture Credit : Google
