Question

A conducting ring of mass 2kg and radius `0.5m` is placed on a smooth plane. The ring carries a current of `i=4A`. A horizontal magnetic field `B=10 T` is switched on at time `t=0` as shown in fig The initial angular acceleration of the ring will be
.
A. `40pirad s^-2`
B. `20pirad s^-2`
C. `5pirad s^-2`
D. `15pirad s^-2`

Answer 1

Correct Answer - a
Due to torque of magnetic field, ring will rotate about vertical
diameter. `tau=Ialphaimplies MB=Ialpha`
`implies ipir^2B=1/2mr^2alpha`
`implies alpha=(2iBpi)/m=(2xx4xx10pi)/2=40pi rads^-2`