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

Concept:
As the magnet falls through the conducting ring, magnetic flux through the ring changes. This induces current in the ring, and by Lenz's law the induced current opposes the motion causing the change. ip

Step 1: Apply Lenz's law.
When the magnet approaches and passes through the copper ring, induced current is produced. This current generates a magnetic field that opposes the relative motion of the magnet. ip

Step 2: Find the effect on acceleration.
Because the magnetic interaction opposes the fall, the net downward acceleration is reduced. So the acceleration becomes less than \(g\). ip Hence, the correct answer is:
\[ \boxed{(B)\ \text{less than acceleration due to gravity}} \]