A conducting circular loop is placed in a uniform magnetic field, `B=0.025T` with its plane perpendicular to the loop. The radius of the loop is made to shrink at a constant rate of `1 mms^(-1)`. The induced emf when the radius is `2 cm` is

Options

A. `2 pi mu V`
B. `pi mu V`
C. `(pi)/(2)mu V`
D. `2mu V`

Answer

B

Explanation

`phi =(B)(pir^(2))implies e=(dphi)/(dt)=(B)(2pir)((dr)/(dt))`
`=(0.025)(2pi )(2xx10^(-2)(10^(-3))=pimuV`