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A conducting loop of finite resistance lies on the x-y plane. There is a constant magnetic field in the z direction. The area of the loop varies with time t, as $A=A_0(1+\sin t)$ in appropriate units. The figure that correctly indicates the qualitative behaviour of the power P dissipated in the loop as a function of time is:
Detailed Solution
$\phi=BA=BA_0(1+\sin t)$. $e=-\frac{d\phi}{dt}=-BA_0\cos t$, so $P=\frac{e^2}{R}=\frac{B^2A_0^2\cos^2t}{R}$, i.e. $P\propto\cos^2t$. P starts at its maximum at t = 0 and falls to zero periodically.