Ans. TRANSMISSION OF ELECTRICAL SIGNAL THROUGH WIRES
A simple telephone model sends voice in the form of electrical signal from one place to another. It consists of a metal reed, an electric coil, and a vibrating diaphragm. Modern telephone also uses diaphragms to turn voices into electrical signal that are transmitted over phone lines. Telephone symbols has two parts:
(i) mouthpiece
(ii) earpiece
The mouthpiece and receiver contain carbon granules and a thin metal diaphragm, When we speak into the earpiece, the sound vibrations also vibrate the diaphragm. A slight vibration of the diaphragm compresses the carbon and thus an electrical current can flow through the wire.
The process is reversed at the other end of the line by the receiver. The electrical current flowing through an electromagnet in the receiver produces a varying magnetic field. This magnetic field attracts the thin metal diaphragm in the receiver, causing.it to vibrate. This vibration of the diaphragm produces sound waves.