A bar magnet is held perpendicular to a uniform field. If the couple acting on the magnet is to be halved, by rotating it, the angle by which it is to be rotated is

Step-by-step solution

The torque acting on a bar magnet in a uniform magnetic field is given by = MB , where M is the magnetic moment, B is the magnetic field, and is the angle between the magnetic moment vector and the magnetic field vector. Initially, the magnet is held perpendicular to the field, so ₁ = 90^ . The initial torque is ₁ = MB 90^ = MB . The problem states that the torque is to be halved, so the new torque ₂ = MB 2 . Substituting the new torque into the formula: MB 2 = MB ₂ , which simplifies to ₂ = 1 2 . This gives ₂ = 30