In a vacuum, two small charged metal spheres A and B are placed as shown in Fig. 4.1. The separation between their centres is $12.0\,\text{cm}$. The charge on each sphere may be treated as a point charge at the sphere’s centre. Point P is a movable point on the straight line joining the centres of the spheres, and its distance from the centre of sphere A is $x$. Fig. 4.2 shows how the electric field strength $E$ at P varies with distance $x$.
(a(i))[1]
State the evidence shown in Fig. 4.2 that supports the claim that the spheres are conductors.
(a(ii))[2]
State the evidence shown in Fig. 4.2 that the charges on the spheres are the same sign, either both positive or both negative.
(b(i))[1]
State the relationship between electric field strength $E$ and the potential gradient at a point.
(b(ii)-1)[2]
Use Fig. 4.2 to state and explain the value of $x$ at which the rate of change of potential with distance is greatest.
(b(ii)-2)[2]
Use Fig. 4.2 to state and explain the value of $x$ at which the rate of change of potential with distance is least.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Electric field strength is zero within the spheres” …