A current loop of magnetic moment $ 0.5 \, \text{Am}^2 $ is placed in a magnetic field of $ 0.4 \, \text{T} $. If the loop is rotated from an angle of $ 0^\circ $ to $ 180^\circ $, what is the change in potential energy?}
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The work done in rotating a dipole from $ \theta_1 $ to $ \theta_2 $ is always $ \Delta U = MB(\cos \theta_1 - \cos \theta_2) $. For a $ 180^\circ $ rotation from the stable equilibrium ($ 0^\circ $), the work is always $ 2MB $.