Question

Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.

Answer 1

The process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction. In practice, we can induce the current in a coil either by moving it in a magnetic field or by changing the magnetic field around it.

Experiment

Take two different coils of copper wire having a large number of turns (say 40 and 90 turns respectively). Insert them over a non-conducting cylindrical roll, as shown in the figure given below. Connect the coil-1, having a larger number of turns, in series with a battery and a plug key

Also, connect the other coil-2 with a galvanometer as shown in the figure. Plugin the key. Observe the galvanometer. We will observe that the needle of the galvanometer instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil-2.

Disconnect coil-1 from the battery. You will observe that the needle momentarily moves but to the opposite side. It means that now the current flows in the opposite direction in coil-2.

This shows that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.