A uniform but time-varying magnetic field B(t) exists in a circular region of radius a and is directed into the plane of the paper, as shown. The magnitude of the induced electric field at point P at a distance r from the centre of the circular region

Options

A. zero
B. decreases as `//r`
C. increases as `r`
D. decreases as `1//r^(2)`

Answer

B

Explanation

`ointvec(E).vec(dt)=(dphi)/(dt)=(d)/(dt)(BA)=(dB)/(dt)A=(dB)/(dt).pia^(2)`
`E.2pir=(dB)/(dt).pia^(2)`
`Eprop1//r`