a b c d

b

$\text{Induced Emf} = \frac{\text{Change in magnetic flux}}{time} = \frac{-\Delta\phi}{t} = \frac{-n(W_2-W_1)}{t}$ $\text{Induced Current}= \frac{\xi}{5R} = \frac{-n(W_2-W_1)}{5Rt}$