From the diagram given below, when the circuit is switched ON, the electric current passed through the coil or solenoid. By the phenomenon of magnetic effect of current, the coil gets magnetized which attracts nearby soft iron armature and the hammer strikes the gong to produce a sound. Thus, the bell starts ringing. When the switch is brought to OFF state, the current flow stops and the magnetisation of coil stop. So, the bell stops ringing.