Electric bells help us by producing sound energy. The energy starts as chemical energy in the batteries. Inside the batteries the chemicals react together to produce electricity. This electrical energy is then changed to moving (kinetic) energy by passing it through something called an electromagnet, which makes the bell clapper move. The clapper then hits a bell to produce sound energy.
An electromagnet is a piece of iron with a coil of insulated wire wrapped around it. If an electric current from a battery is passed through the coil then the piece of iron becomes a magnet which can then attract a second piece of iron towards it, so producing movement. If the electricity is switched off then the iron is no longer a magnet and so the second piece of iron is no longer attracted to it.
If this second piece of iron is the clapper for the bell then when it is attracted to the electromagnet it can also be made to strike the bell. If this same piece of iron is also the switch that turns the electricity on and off then after it has struck the bell the circuit is broken, the electromagnet is no longer magnetised so it moves away from the bell, switches the electromagnet back on and so is attracted towards the bell again. This process continues so making the bell ring continuously.
A second (push) switch is included in the circuit, this being the one that you would push to start the bell ringing.