A current loop in a magnetic field

When a current loop is placed in a magnetic field it experiences a torque. It is given by$\overrightarrow{\tau }=\overrightarrow{M}\times \overrightarrow{B}$

Where $\overrightarrow{M}$is the magnetic moment of the loop and$\overrightarrow{B}$is the magnetic field.

or $\tau =MB\sin \theta$ where $\theta$ is angle between M and B

When $\overrightarrow{M}$ and $\overrightarrow{B}$ are parallel (i.e. $\theta$ = 0°) the equilibrium is stable and when they are antiparallel (i .e. $\theta =\mathrm{\pi }$) the equilibrium is unstable.