Question

A bar magnet is released into a copper ring directly below it. The acceleration of the magnet will be

• A. equal to the acceleration due to gravity at that place
• B. less than the acceleration due to gravity at that place
• C. greater than the acceleration due to gravity at that place
• D. twice the acceleration due to gravity at that place

Hint:

Induced currents always oppose the cause producing them.

Answer 1

The Correct Option is B

When a bar magnet is released into a copper ring directly below it, an interesting physical phenomenon known as electromagnetic induction occurs. Let's analyze the situation to determine the acceleration of the magnet:

1. As the bar magnet moves towards the copper ring, the magnetic flux passing through the ring changes. According to Faraday's law of electromagnetic induction, a change in magnetic flux induces an electromotive force (EMF) in the ring.
2. This induced EMF causes a current to flow in the copper ring. Due to Lenz's law, the direction of this induced current will be such that it opposes the change in magnetic flux causing it.
3. The current in the ring generates its own magnetic field, which opposes the motion of the bar magnet. This opposition is a manifestation of Lenz's law, which states that the direction of induced current will always oppose the change in flux that produced it.
4. The opposing magnetic field exerts a force on the bar magnet. This force is called a magnetic damping force, and it acts upwards, opposing the gravitational force pulling the magnet downwards.
5. As a result of this opposing force, the net downward force acting on the magnet is less than the gravitational force alone.
6. Since acceleration is directly proportional to force (as per Newton's second law: F = ma), the net force acting on the magnet is reduced, leading to a reduction in the magnet's acceleration.

This detailed analysis shows that the acceleration of the magnet is less than the acceleration due to gravity. Other options are incorrect because:

• If the force were only due to gravity, no other forces would act on the magnet, leading to acceleration equal to the gravitational acceleration.
• There is no additional force acting on the magnet that would cause it to accelerate faster or double the gravitational acceleration.

Correct Answer: The acceleration of the magnet will be less than the acceleration due to gravity at that place.