A 250 -Turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85  μA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180 ° against the torque is:

Step-by-step solution

W = M B   cos ⁡ θ 1 - cos ⁡ θ 2 When it is rotated by angle 180 o then θ 1 = 0 ° and θ 2 = 180 ° W = 2 M B W = 2 N I A B = 2 × 250 × 85 × 10 - 6   1.25 × 2.1 × 10 - 4 × 85 × 10 - 2 = 9.1   μJ