Question

Figure shows a fixed coil of several turns connected to a centre zero galvanometer (G) and a magnet (N S) which can move.

(a) Describe the observation in the galvanometer if (i) the magnet is moved rapidly in the direction of the arrow, (ii) the magnet is kept still after it has moved into the coil, and (iii) the magnet is then rapidly pulled out the coil.

(b) How would the observation alter if a more powerful magnet is used?

Answer 1

(a) 

1. When the magnet is moved rapidly towards the coil, the magnetic flux through the coil increases. The galvanometer deflects in one direction (say, right).
2. When the magnet is kept still inside the coil, there is no change in magnetic flux, so the galvanometer shows no deflection (zero).
3. When the magnet is rapidly pulled out, the flux decreases. The galvanometer deflects in the opposite direction (say, left).

(b) If a more powerful magnet is used, the rate of change of magnetic flux is greater, so the induced e.m.f. and current are larger. The galvanometer deflection will be larger in both cases.