A metal wire of uniform cross-sectional area $1 {\mathrm{mm}}^2$ has a free electron density of $6\times {10}^{28} {\mathrm{m}}^{-3}$. If the wire is carrying $0.96 \mathrm{A}$ current, what is the drift velocity of the free electrons along the wire? (Charge on electron$=1.6\times {10}^{-19} \mathrm{C}$).

In the circuit shown here, $E_1=E_2=E_3=2 \mathrm{V}$ and $R_1=R_2=4 \text{Ω}$. The current flowing between points $A$ and $B$ through battery $E_2$ is

The following figures show four situations, in which positive and negative charges move horizontally through a region and give the rate at which each charge moves. Rank the situations according to the effective current through the region greatest first.