A circular coil of radius $\mathrm{4 }\mathrm{c}\mathrm{m}$ having $50$ turns carries a current of $2 \mathrm{A}$. It is placed in a uniform magnetic field of the intensity of $0.1\mathrm{ }\mathrm{W}\mathrm{e}\mathrm{b}\mathrm{e}\mathrm{r} {\mathrm{m}}^{-2}$. The work done to rotate the coil from the equilibrium position by $180°$ is