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. `3.2pimuV`
B. `4.8pimuV`
C. `0.8pimuV`
D. `1.6pimuV`

Answer

A

Explanation

`phi=BA=Bpir^(2)`
`e=(dphi)/(dt)=Bpi.2r(dr)/(dt)=0.04pixx2xx2xx10^(-2)xx2xx10^(-3)`
`=3.2pimuV`