A circular coil of 100 turns and effective diameter `20cm` carries a current of `0.5A`. It is to be turned in a magnetic field of `B=2.0T` from a position in which the normal to the plane of the coil makes an angle `theta` equals to zero to one in which `theta` equals to `180^(@)`. Thw work required in this process is
A. `pi J`
B. `2pi J`
C. `4 pi J`
D. `8 pi J`
