A conducting circular loop is placed in a uniform magnetic field `0.04T` with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at `2mm//sec` . The induced emf in the loop when the radius is `2cm` is

Options

A. `1.6 pi mu v`
B. `3.2 pi mu v`
C. `4.8 pi mu v`
D. `0.8 pi mu v`

Answer

B

Explanation

`e=( d phi)/(dt)=(d)/(dt)(B pir^(2))`
`=2 pi B(dr)/(dt)`
`= 2 xx pi xx 2 xx 10^(-2) xx 4 xx 10^(-2) xx 2xx 10^(-3)`
`=3.2 xx 10^(-6) pi Vol=3.2pi muV `