Question

A bar magnet having a magnetic moment of 2 × 10⁴ JT^–1 is free to rotate in a horizontal plane. A horizontal magnetic field B = 6 × 10^–4 Tesla exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction 60° from the field is

(a) 0.6 J 

(b) 12 J 

(c) 6 J 

(d) 2 J

Answer 1

The correct option (c) 6J

Explanation:

Work done = MB(1 – cosθ)

Given  : M = 2 × 10⁴ J/T

B = 6 × 10^–4 T

θ = 60°

∴ w = 2 × 10⁴ × 6 × 10^–4 (1 – cos60°)

= 12[1 – (1/2)]

w = 6J