The charge flowing in a conductor varies with time as Q = at - bt2, then the current:

reaches a maximum and then decrease falls to zero after t = $\frac{a}{2b}$ changes at a rate of (-2b) both (2) and (3)

both (2) and (3)

According to question, $\mathrm{Q}=\mathrm{at}-\mathrm{bt}^2 \Rightarrow \mathrm{i}=\frac{\mathrm{dQ}}{\mathrm{dt}}=\mathrm{a}-2 \mathrm{bt}$ $\mathrm{i}=0 \text { at } \mathrm{t}=\frac{\mathrm{a}}{2 \mathrm{b}}$ $\frac{\mathrm{di}}{\mathrm{dt}}=-2 \mathrm{b}$