Question

A copper ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. Then, the acceleration of the falling magnet (neglect air resistance) will be.
A) Equal to g
B) Less than g
C) Greater than g.
D) Zero.

Answer 1

Hint: The famous example is of a bar magnet moving to and fro in the solenoid. We all have seen that when the bar magnet is moved in between the solenoid a current is induced in it which opposes the change of in the bar magnet. Here instead of a solenoid there is a coin and the bar magnet going towards the ring is accelerating with g which is the gravitational acceleration. Apply the above mentioned concept and choose the correct option.

Complete step by step solution:
Here there would be an acceleration when the bar magnet would flow through the copper ring. The ring is made up of metal so when the magnet passes through the axis of the ring there would be a current induced in the ring and according to Lenz law the current induced in a circuit is such that it opposes the change through which it is induced. Here the current that is induced in the copper ring will oppose the change, that is it will oppose the motion of the bar magnet going through it and hence the acceleration will decrease. So, the acceleration would be less than the gravitational acceleration.

Hence, Option (B) is correct.

Note: Here we have to imagine a ring and a magnet going in between the rings. Apply the concept proposed by Emil Lenz. The current induced will oppose the change through which it is produced.