Question

A bar magnet of dipole moment 10⁴ JT^–1 is free to rotate in a horizontal plane. A horizontal magnetic field 4 × 10^–5 T exists in the space. Find the work done in rotating the magnet slowly from a direction parallel to the field to a direction 60⁰ from the field –

• A. 0.1 J
• B. 0.2 J
• C. 0.4 J
• D. 0.5 J

Answer 1

Answer: (B)

0.2 J

Answer 2

W = MB (cos 0⁰ – cos 60⁰) = $\frac { \mathrm { MB } } { 2 }$