A long, narrow bar magnet that has magnetic moment m parallel to its long axis is suspended at its center as a frictionless compass needle. When placed in a magnetic field B, the needle lines up with the field. If it is displaced by a small angle θ, show that the needle will oscillate about its equilibrium position with frequency f = (1/2)π √μB/I, where I is the moment of inertia about the point of suspension.