Figure shows a bar magnet suspended by a thin wire that provides a restoring torque -??. The magnet is 16 cm long, has a mass of 0.8 kg, a dipole moment of ? = 0.12 A???m2, and it is located in a region where a uniform magnetic field B can be established. When the external magnetic field is 0.2 T and the magnet is given a small angular displacement ??, the bar magnet oscillates about its equilibrium position with a period of 0.500 s. Determine the constant ? and the period of this torsional pendulum when B = 0.

W. B