A bar magnet having a magnetic moment of 2 10^4 JT ⁻¹ is free to rotate in a horizontal plane. A horizontal magnetic field B =6 10⁻⁴ ~T exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction 60^ from the field is

Step-by-step solution

Key Idea The work done in rotating a magnetic dipole against the torque acting on it, when placed in magnetic field is stored inside it in the form of potential energy. When magnetic dipole is rotated from initial position = ₁ to final position = ₂ , then work done = MB ( ₁- ₂ ) aligned & = MB (1- 1 2 ) & = 2 10^4 6 10⁻⁴ 2 =6 ~J aligned