(a)[2]
For any location outside a spherical conductor, the charge on the sphere can be treated as though it were a point charge at the centre. Use electric field lines to explain why.
(b)
An isolated spherical conductor carries charge $q$, as shown in Fig. 6.1. Point $P$ is a movable point which, at any one time, is a distance $x$ from the centre of the sphere. The way the electric potential $V$ at point $P$, due to the charge on the sphere, varies with distance $x$ is shown in Fig. 6.2.
(b(i))[3]
Use Fig. 6.2 to find the electric field strength $E$ at point $P$ when $x = 6.0\,\text{cm}$.
(b(ii))[2]
Find the radius $R$ of the sphere. Explain your answer.