Explain the working of an electric bell in brief.

An electric bell works on the principle of electromagnetism.

An electric bell consists of an electric source (battery), a switch,  electromagnet, a soft iron armature, a striker or hammer, and a gong.

When the switch is turned on, electric current flows through the coils, and the metal arms (or iron rods) generates a magnetic field that attracts the iron strip attached to a striker. The striker hits the gong (bell) and makes it ring. 

Simultaneously, its contact with the screw is broken, so the circuit is also broken and the current flowing through the electromagnet stops. As such, the iron strip returns to its original position the contact is restored and current start flowing through the electromagnet again. This phenomenon repeats many times in a second, and it rings till the circuit has been switched off.