Q. Working of On - off hook circuit in telephone hand set?

On/off hook circuit (sometimes termed as a switch hook) is nothing more than a simple single-throw, double-pole (STDP) switch placed across tip and ring. Switch is mechanically connected to telephone handset so that when telephone is idle (on hook), switch is open. When telephone is in use (off hook), switch is closed completing and electrical path through microphone between tip and ring of local loop.