Question

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

Reason : Magnetic moment depends on area of the loop.

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not correct explanation of A

(c) A is true but R is false

(d) A and R are false

Answer 1

Correct option (a) Both A and R are true and R is the correct explanation of A

Explanation:

Magnetic dipole moment of the current loop = Ampere turns x Area of the coil

or M = NIpr²

When radius of the coil becomes double. new magnetic moment will be

M₁  = NIp(2r)² = 4NIr²p = 4M

Hence magnetic moment becomes four times when radius is doubled.