Question

A light copper ring is freely suspended by a light string. A bar magnet is held horizontally with its length along the axis of the ring. The magnet is moved towards the ring with its N pole facing the loop. What will happen to the ring and its position? Explain.

Hint:

In the case of electromagnetic induction, when a magnet is moved near a conducting loop, a current is induced in the loop that creates a magnetic field opposing the magnet's motion, according to Lenz's Law.

Answer 1

Effect on a Suspended Copper Ring When a Magnet is Moved Towards It
Consider a light copper ring freely suspended by a light string. A bar magnet is held horizontally such that its axis coincides with the axis of the ring. The magnet is moved towards the ring with its north pole facing the ring.

Step 1: Change in Magnetic Flux
When the north pole of the magnet is brought closer to the ring, the magnetic field through the ring increases.
This causes a change in magnetic flux linked with the ring.
According to Faraday’s Law of Electromagnetic Induction:
An induced current is produced in the ring whenever there is a change in magnetic flux through it.

Step 2: Direction of Induced Current (Lenz’s Law)
According to Lenz’s Law:
The direction of induced current is such that it opposes the cause producing it.
Here, the cause is the increasing magnetic flux due to the approaching north pole.
So, the induced current will flow in such a direction that the face of the ring near the magnet behaves like a north pole (to oppose the approaching north pole).
Thus, like poles face each other → repulsion occurs.

Step 3: Effect on the Ring
- The ring will be repelled by the approaching magnet.
- It will move away from the magnet due to magnetic repulsive force.
- Its suspended position will shift slightly backward (away from the magnet).

If the Magnet is Held Stationary:
When the magnet stops moving, magnetic flux becomes constant.
No change in flux → No induced current → No force.
The ring returns to its normal hanging position.

Conclusion:
When the north pole of the magnet is moved towards the copper ring, an induced current is produced in such a direction that the ring develops a north pole facing the magnet. As a result, the ring is repelled and moves away from the magnet due to Lenz’s Law.