The pole strength qm of a bar magnet is defined by qm = ||/L, where L is

The pole strength qm of a bar magnet is defined by qm = |μ|/L, where L is the length of the magnet. Show that the torque exerted on a bar magnet in a uniform magnetic field B is the same as if a force +qm B is exerted on the north pole and a force –qmB is exerted on the south pole.