A simple push button electric bell is one of the simplest electric circuits wih a real use. It consists of an coil wound on an electromagnet, next to which is a soft iron (so easily magnetized) armature and a hammer poised to strike a bell.
When the switch is pressed the circuit is complete and a current flows. The electromagnet then produces a magnetic field, magnetizing the soft iron armature and attracting it. This forces the hammer to strike the gong. When this happens the circuit is broken – this time by the spring attached to the armature.
Current stops flowing and the electromagnetic becomes demagnetized and ceases to attract the soft iron armature which then springs back to remake the circuit. The circuit is broken and remade many times per second until the switch is released.