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. The acceleration of the falling magnet while it is passing through the ring is

• A. more than acceleration due to gravity.
• B. less than acceleration due to gravity.
• C. depends on the diameter of ring and length of magnet.
• D. depends on pole strength of magnet.

Hint:

In induction problems, Lenz's law always opposes the cause producing the flux change.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Lenz's Law states that an induced current always flows in a direction that opposes the change in magnetic flux that produced it.
Step 2: Detailed Explanation:
1. As the magnet approaches the ring, flux through the ring increases. The induced current creates a field that repels the incoming magnet.
2. As the magnet passes through the center and starts leaving, flux decreases. The induced current creates a field that attracts the magnet back towards the ring.
In both cases, there is an upward magnetic force acting on the magnet. This force opposes the downward force of gravity.
Net acceleration $a = \frac{mg - F_{magnetic}}{m} = g - \frac{F_{magnetic}}{m}$.
Thus, $a<g$ always.
Step 3: Final Answer:
The acceleration is less than acceleration due to gravity.