A conducting ring of mass 2 Kg and radius $0.5m$ is placed on a smooth horizontal surface. The ring carries a current $i = 10A$. A horizontal magnetic field $B = 4T$ is now switched on. The angular acceleration of the ring will be

Question

$\begin {array} {1 1} (a)\;10 \pi \: rad/s^2 & \quad (b)\;20 \pi \: rad/s^2 \\ (c)\;30 \pi \: rad/s^2 & \quad (d)\;40 \pi \: rad/s^2 \end {array}$