A circular coil of $100$ turns and effective diameter $20 \mathrm{cm}$ carries a current of $0.5 \mathrm{A}$. It is to be turned in a magnetic field of $B=2 \mathrm{T}$ from a position in which the normal to the plane of the coil making an angle $\mathrm{\theta }$ with magnetic field changes from $\mathrm{\theta }=0^{°}$ to $\theta ={180}^{\mathrm{o}}$ . The work required in this process is