question_answer

A magnet N-S is suspended from a spring and when it oscillates, the magnet moves in and out of the coil C. The coil is connected to a galvanometer G. Then, as the magnet oscillates:

A)  G shows no deflection

B)  G shows deflection to the left and right but the amplitude steadily decreases

C)  G Shows deflection to the left and right with constant amplitude

D)  G shows deflection on one side.

Correct Answer: B

Solution :

When the S-pole of a magnet is moved towards the coil, then by Lenzs law the face of coil, towards magnet becomes S-pole and the current flows clockwise to cancel change in the magnetic flux. So, to bring the magnet near to the coil, more work has to be done against the force of repulsion produced between them. So, the galvanometer shows deflection to the left. Now when the S-pole is moved away, a current flows in anti-clockwise direction to make the face of the coil towards magnet, a N-pole. Thus, will try to attract the magnet. So, the galvanometer shows the deflection to the right. Since, flux varies hence, amplitude will not be constant and will decrease.