Physics - Magnetism Question with Solution | TestHub

Magnetic potential of a bar magnet in external magnetic field is given by $U=-MB\cos \theta$ Here, $M=0.15\mathrm{J}/\mathrm{T},B=0.4\mathrm{T}$, and $\theta =180^{\circ }$ as magnet is in unstable equilibrium. $\begin{array}{rl}\therefore U& =-0.15\times 0.4\times \cos 180^{\circ }\\ & =-0.15\times 0.4\times (-1)\\ & =6\times 10^{-2}\mathrm{J}\end{array}$