A uniform conducting ring of mass `pi` kg and radius 1 m is kept on smooth horizontal table. A uniform but time varying magnetic field `B = (hat (i) + t^(2) hat (j))T` is present in the region, where t is time in seconds. Resistance of ring is `2 (Omega)`. Then

Time (in second) at which ring start toppling is

Options

A. `(10)/(pi)sec`
B. `(20)/(pi)sec`
C. `(5)/(pi)sec`
D. `(5)/(pi)sec`

Answer

A

Explanation

`I=(1)/(R)|(dphi)/(dt)|=(1)/(2)pixx1^(2)::2t=pit`
The ring will start toppling when
`tau_(m)=tau_(g)`
`impliesIAB_(x)=mgr`
`impliespitxxpixx1^(2)xx1=pixx10xx1`
`impliest=(10)/(pi)sec`