JEE Main · 2021 · 20 Jul 2021 · Shift 1 · Electromagnetic Induction

The field occupies only the strip from $x=0$ to $x=b$. While the arm sweeps across this strip the area linked with the field grows uniformly, so the flux rises linearly; from $x=b$ to $x=2b$ no further field is swept and the flux stays constant, and on the return crossing of the strip it falls linearly back. The induced emf is $-\frac{d\Phi }{dt}$, so it is a constant of one sign during the outward crossing, zero while the arm is outside the strip, and a constant of the opposite sign during the return crossing. The power dissipated is $\frac{{\epsilon }^2}{R}$, which is insensitive to that sign change, so it appears as two equal positive pulses separated by a zero interval. In the figure, the graph marked A is therefore the flux, the graph marked B is the induced emf and the graph marked C is the power dissipated.