Question

A conducting loop of radius $R$ is present in an uniform magnetic field $B$ perpendicular to the plane of the ring. If radius $R$ varies as a function of time $‘t^{\prime }$, as $R=R_0+t$. The e.m.f induced in the loop is

• A. $2\pi (R_0+t)B$ clockwise
• B. $\pi (R_0+t)B$ clockwise
• C. $2\pi (R_0+t)B$ anticlockwise
• D. Zero

Answer 1

The correct option is C $2\pi (R_0+t)B$ anticlockwise

$\varphi =B.\pi (R_0+t{)}^2\cos 0^{\circ }$
$E=-\frac{d\varphi }{dt}=-2B\pi (R_0+t)$

Since increasing radius increases flux into the plane, e.m.f. induced is anticlockwise.