Two tiny solid metal spheres A and B, each with the same radius, are in a vacuum. Their centres are 15\ \text{cm} apart. Sphere A carries a charge of +3.0\ \text{pC} and sphere B carries +12\ \text{pC}. Fig. 5.1 shows the arrangement. Point P lies on the line joining the centres of the spheres, at a distance of 5.0\ \text{cm} from the centre of sphere A.
(a)[2]
Suggest why the electric field strength is zero inside both spheres.
(b)[3]
Show that the electric field strength is zero at point P. Explain your working.
(c)[2]
Calculate the electric potential at point P.
(d)[3]
A silver-107 nucleus $^{107}_{47}\text{Ag}$ has speed $v$ when it is a long distance from point P. Use your answer in (c) to calculate the minimum value of speed $v$ needed for the nucleus to reach point P.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “If an electric field were present in a conductor, charges would move” …