A Telephone system is a communication instrument that transmits any voice / sound signals to far by locations by converting these sound signals in waves and receives and reconverts the same waves into sound signals/ voice. The telephone network is extended universally so if you want to talk to someone, you simply need to pick up the telephone system and dial a few digits. You are instantly connected to that person and both of you can have a 2 way conversation.
Telephone systems were first introduced by Graham Bell over one hundred years ago, but it is still works on the same operating principle. To make a call, we need to first pick up the handset. This causes the telephone system to be connected to a routing network. By pressing the numbers present on the touch tone keypad / frequency generator, signals are passed down via phone line to the routing station. Here, each digit is identified as a unique combination of tone frequencies. The specific combination of digits causes a signal to be passed to other telephone systems causing it to ring. When that telephone is picked up, connection between the two telephone systems is achieved.
The ear piece acts as speaker where as mouthpiece acts as a microphone. Sound waves from the user’s voice cause vibration to a thin plastic disc present inside the telephone system. This causes change in the distance between the plastic disk and another metal disk resulting in a varying electric current which is passed through the phone lines. The receiver on the other phone picks up this electromagnet current. These magnets cause diaphragm to vibrate which produces the sound /voice that initiated the current. An amplifier in the receiver end makes it easier to hear. When one of the phones is hung up the electric current get broken resulting in dis-connection of the telephone systems.