Question

A coil of insulated copper wire is connected to galvanometer. What would happen if a bar magnet is
(i) pushed into the coil?
(ii) withdrawn from inside the coil?
(iii) held stationary inside the coil?

Answer 1

(i) The magnetic flux linked with the coil changes (i.e., increases). As a result of this, an induced current flows in the coil and the galvanometer shows a momentary deflection (say towards right) i.e., the needle of the galvanometer moves momentarily in one direction.
(ii) The magnetic flux linked with the coil changes (i.e., decreases). As a result of this, an induced current flows in the coil but in a direction opposite to that in case (i). Obviously, the galvanometer momentary shows a deflection in the opposite direction (i.e., towards left) i.e., the needle of the galvanometer moves momentary but in the opposite direction to (i).
(iii) When the magnet is held stationary in the coil, there will be a magnetic flux in the coil but it will remain constant. Since the magnetic flux does not change, there is no induced current in the coil and the galvanometer shows no deflection.