A bar magnet having a magnetic moment of 2 x 10⁴JT⁻¹ is free to rotate in a horizontal plane. A horizontal magnetic field B = 6 x 10⁻⁴T exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction 60⁰ from the field is

Options

(a) 12 J
(b) 6 J
(c) 2 J
(d) 0.6 J

Correct Answer:

6 J

Explanation:

Work done
= MB (cos θ₁ – cos θ₂)
= MB (cos 0⁰ – cos 60⁰)
= MB (1 – 1/2) = 2 x 10⁴ x 6 x 10⁻⁴ /2 = 6 J