Q: A magnet is suspended at an angle 60° in an external magnetic field of 5 × 10-4 T. What is the work done by the magnetic field in bringing it in its direction ? [The magnetic moment = 20 A-m2]
Sol: Work done by the magnetic field,
W = MB(cosθ1-cosθ2) ;here θ1 = 60° and θ2 = 0°
∴ W = 20 × 5 × 10-4 [cos60° – cos0°]
= 10-2 [1/2-1]
= -5 × 10-3 J