A bar magnet having a magnetic moment of 2 . 0 × 10 5 J T - 1 , is placed along the direction of uniform magnetic field of magnitude B = 14 × 10 - 5 T . The work done in rotating the magnet slowly through 60 ° from the direction of field is

Step-by-step solution

Work done by the external force is equal to the change in the potential energy, W e x t = Δ U = U f - U i ⇒ W e x t = - M B cos θ 2 + M B cos θ 1 ⇒ W e x t = M B cos θ 1 - cos θ 2 ⇒ W e x t = 14 × 10 - 5 × 2 × 10 5 cos 0 ° - cos 60 ° ⇒ W e x t = 14 × 2 × 1 2 = 14   J