Moving Charges And Magnetism

A circular coil of 100 turns has an effective radius of 0.05 m and carries a current of 0.1 A. How much work is required to turn it in an external magnetic field of 1.5 Wb/m through 180° about its axis perpendicular to the magnetic field? The plane of the coil is initially perpendicular to the magnetic field.

A coil in the shape of an equilateral triangle of side is suspended between the pole pieces of a permanent magnet such that is in the plane of the coil. If due to current in the triangle, a torque acts on it. The side of the triangle is