Question

Assertion (A): When radius of a current carrying loop is doubled, its magnetic moment becomes four times.

Reason (R): The magnetic moment of a current carrying loop is directly proportional to the area of the loop.

Options

• Both (A) and (R) are true, and (R) is correct explanation of (A).

• Both (A) and (R) are true, and (R) is not correct explanation of (A).

• (A) is true, but (R) is false.

• (A) is false and (R) is also false.

Answer 1

Both (A) and (R) are true, and (R) is correct explanation of (A).

Explanation:

The relationship between current and magnetic moment of a current-carrying loop is M = IA

A = πR²

So, M ∝ R²

This means that if you double the radius, the moment will be four times as big. The assertion is true.

Since M = IA,

∴ M ∝ A

The reason is true. Also, reason is the proper explanation of the assertion.