Explain a simple demonstration for the production of eddy current.

Explanation

Let us consider a pendulum that can be made to oscillate between the poles of a powerful electromagnet (fig (a)).
First the electromagnet is switched off, the pendulum is slightly displaced and released. It begins to oscillate and it executes a large number of oscillations before stopping. The air friction is the only damping force. When the electromagnet is switched on and the disc of the pendulum is made to oscillate, eddy currents are produced in it which will oppose the oscillation. A heavy damping force of eddy currents will bring the pendulum to rest within a few oscillations (figure (b)). However if some slots are cut in the disc as shown in the (figure (c)) eddy currents are reduced. The pendulum now will execute several oscillations before coming to rest. This clearly demonstrates the production of eddy current in the disc of the pendulum.