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. `4.8 pimuV`
B. `0.8pi mu V`
C. `1.6 pi mu V`
D. `3.2 pi mu V`

Answer

D

Explanation

Area of the circel is given by
`a=pir^(2)`
The rate of change of area is
`(da)/(dt)=2pirxx(dr)/(dt)`
So, the induced emf
`e=(d phi)/(dt)=Bxx(da)/(dt)`
`=0.04xx2pixx2xx10^(-2)xx10^(-3)=3.24pimuV`