Question

An iron rod of length L and magnetic moment M is bent in the form of a semicircle Now its magnetic moment will be 

(a) M 

(b) (2M/π)

(c) (M/π) 

(d) Mπ

Answer 1

The correct option (b) (2M/π)

Explanation:

We know, magnetic moment = M= m × ℓ (1) 

when wire is bent, the pole strength remains same & when it is in the form of semicircular arc, the separation between poles in 2r. (r is radius of semicircle)

∴ πr = ℓ 

∴ r = (ℓ/π)

∴ New magnetic moment = M' = m × 2r 

= m × (2ℓ/r)

= (2M/π) from (1)