Q.The potential energy of a magnetic dipole whose dipole moment is $\vec{p}_m = (-0.5\hat{i} + 0.4\hat{j})\ \text{Am}^2$ kept in uniform magnetic field $\vec{B} = 2\hat{j}\ \text{T}$ :

Rotating a magnetic dipole against its restoring torque, from a reference angle of $90°$ to a general angle $\theta$ with a uniform field $\vec B$, stores potential energy

This is minimum, $U=-p_mB$, when the dipole is aligned with the field ($\theta=0°$) -- the stable equilibrium -- and maximum, $U=+p_mB$, when it is anti-aligned ($\theta=180°$) -- the unstable equilibrium. The work needed to flip a dipole from the st …