Electric current has both magnitude and direction. It is a

$A$ current of $20\,\mu A$ flows for $30$ seconds in a wire. The total charge transferred will be:

An electron revolves $6 \times 10^{15}$ times per second in a circular loop. The current in the loop is:

The current in a conductor is expressed as $I = 3t^2 + 4t^3$,where $I$ is in Ampere and $t$ is in second. The amount of electric charge that flows through a section of the conductor during $t = 1 \ s$ to $t = 2 \ s$ is . . . . . . $C$.

An electron moves with a constant speed of $4 \times 10^6 \, m/s$ in a circle of radius $10 \, cm$. Find the electric current at any point on the circle.

The charge flowing in a conductor varies with time as $Q = at - bt^2$. Then for current,which statement is incorrect?
$(A)$ decreases linearly with time
$(B)$ reaches a maximum and then decreases
$(C)$ falls to zero after time $t = a/2b$
$(D)$ changes at a rate $-2b$