(a)[1]
State what is meant by the coulomb.
(b)[1]
Electric current consists of moving charge carriers. From the list below, underline the charges that could belong to a charge carrier: $8.0 \times 10^{-19}\,\text{C}$, $4.0 \times 10^{-19}\,\text{C}$, $1.6 \times 10^{-19}\,\text{C}$, $1.6 \times 10^{-20}\,\text{C}$.
(c)[2]
As shown in Fig. 6.1, the diameter of wire $ST$ changes linearly with distance along the wire. A current $I$ flows in the wire. At the $S$ end, the diameter is $d$ and the mean drift speed of the free electrons is $v_s$. At the $T$ end, the diameter is $2d$. On Fig. 6.2, sketch a graph to show how the mean drift speed changes with position along the wire from $S$ to $T$.