Question

A copper ring having a cut such as not to form a complete loop is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. Then acceleration of the falling magnet is (neglect air friction)
(A) g
(B) less than g
(C) more than g
(D) 0

Answer 1

Hint: The best example is of a bar magnet moving in a to and fro motion is the solenoid. We are aware of the fact that on moving a bar magnet between the solenoid, a current is induced in it which always opposes the change in the orientation of the bar magnet. In this case, in place of a solenoid, there is a bar magnet going inside the ring and accelerating with an acceleration which is equal to g. Here we will apply this concept and find the correct option.

Complete step by step answer:
In this case, there will be an acceleration when the bar magnet will enter the copper ring. The copper ring is made of metal, this means that when the magnet passes through the axis of the ring a current will be induced in the ring and on applying Lenz law, the current which is induced in the circuit will oppose the change through which it is induced. Thus, the current which is induced inside the copper ring will oppose any change, i.e., it will be opposing the motion of the bar magnet which is going through it and hence the acceleration will decrease.
So, the acceleration will be less than the acceleration due to gravity.

Note: In this case, we have to imagine a ring and a magnet which is going in between the rings. Then, we will apply the concept which was proposed by Emil Lenz. The current which will be induced will oppose the change through which it actually was produced.