A uniform conducting ring of mass `pi` kg and radiius 1m is kept on a smooth horizontal table, A uniform but time varying magnetic field T is present in the region where is in second and the positive y-axis is in vertically upward direction, `(g=10m//s^(2))`. Resistance of the ring in `2Omega`.

Time at which rings starts toppling is

Options

A. `10/(pi)sec`
B. `20/(pi)sec`
C. `5/(pi)sec`
D. `25/(pi)sec`

Answer

A

Explanation

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