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 Lenz's law the face of coil, towards magnet becomes S-pole and the current flows clockwise to cancel charge in the magnetic flux. 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.