Problem 19E

19. The quantity of charge $Q$ in coulombs (C) that has passed through a point in a wire up to time $t$ (measured in seconds) is given by $Q(t)=t^{3}-2 t^{2}+6 t+2$. Find the current when

(a) $t=0.5 \mathrm{~s}$ and $(\mathrm{b}) t=1 \mathrm{~s}$. [See Example 3 . The unit of current is an ampere $(1 \mathrm{~A}=1 \mathrm{C} / \mathrm{s})$.] At what time is the current lowest?