(a) What is electromagnetic induction?

(b) Describe one experiment to demonstrate the phenomenon of electromagnetic induction.

(a) Whenever there is a change in the number of magnetic field lines linked with a conductor, an electromotive force (e.m.f.) is developed between the ends of the conductor which lasts as long as there is a change in the number of magnetic field lines through the conductor. This phenomenon is called the electromagnetic induction.

(b) Demonstration of the phenomenon of electromagnetic induction —

Experiment — Wind an insulated copper wire in form of a spiral on a paper (or wooden) cylinder so as to form a coil in the form of a solenoid. Connect a centre zero galvanometer G between the two ends of the solenoid. Then, place a magnet NS at some distance along the axis of solenoids as shown in figure.

Observations — It is observed that,

(i) When the magnet is stationary, there is no deflection in galvanometer and it's pointer reads zero as shown in figure (a).

(ii) When the magnet with it's north pole facing the solenoid is moved towards it, the galvanometer shows a deflection towards right showing that a current flows in solenoid in the direction B to A as shown in figure (b).

(iii) As the motion of magnet is stopped, the pointer of galvanometer comes to zero position. Fig. (c) This shows that the current in solenoid flows as long as the magnet is in motion.

(iv) If the magnet is moved away from the solenoid, the pointer of galvanometer deflects towards left (as shown in figure d) showing that the current in solenoid flows again, but now in direction A to B which is opposite to that as shown in figure b. Current becomes zero as soon as the magnet stops.

(v) If the same action (movement) of magnet is done rapidly, the deflection in the galvanometer is more than before although the direction of deflection remains same. It shows that now more current flows.

(vi) If the magnet is brought towards the solenoid by keeping it's south pole towards it, the pointer of galvanometer deflects towards left as shown in figure (e) showing that the current in solenoid flows in direction A to B which is opposite to that shown in figure (b)