Q 12-05-080JEE MainJEE Main 2017 (8 Apr)Easy
A magnetic dipole in a uniform magnetic field has: (Take zero potential energy when magnetic dipole is perpendicular to magnetic field)
Answer: (B) Zero potential energy when the torque is maximum
$$U = -mB\cos\theta,\qquad \tau = mB\sin\theta$$
At $\theta = 90^\circ$ (dipole perpendicular to the field) the torque is maximum, $mB$, and $U = 0$. So the dipole has zero potential energy when the torque is maximum.
Solution by Sreeraj P, M.Sc Physics