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. g
• B. more than g
• C. less than g
• D. zero

Answer 1

The correct option is C

less than g

The explanation of the correct option :

Option(C):

The diagrammatic representation of the given situation is:

1. As the magnet moves through the ring, flux through the ring changes
2. According to Lenz Law, a current is produced in the ring that opposes the movement of the magnet
3. The induced current has a magnetic field which decreases the acceleration of the magnet
4. Therefore the speed of the magnet will be less than the acceleration due to gravity
5. This happens regardless of the increase or decrease in flux

The explanation for the incorrect option:

Option (A): The acceleration cannot remain the same since the magnetic field has a decreasing effect on it

Option (B): In no way can the acceleration increase because for that it requires a positive or contributing force which is not provided

Option (D): The acceleration cannot be zero since there is no opposing force greater than g stopping it.

Hence,the correct option C.