(a)[2]
Define electric potential at a point in words.
(b(i))[1]
State how the magnitude of the electric field strength is connected to the potential gradient.
(b(ii))[2]
Use your answer in (i) to show that the force on particle Q is proportional to the gradient of the curve of Fig. 4.2.
(c)[4]
The magnitude of the charge on each of the particles P and Q is $1.6 \times 10^{-19}\text{ C}$. Calculate the separation of the particles at the point where particle Q has electric potential energy equal to $-5.1\text{ eV}$.
(d(i))[2]
Using Fig. 4.2, state and explain whether the two charges have the same sign or opposite sign.
(d(ii))[2]
By reference to Fig. 4.2, state and explain the effect, if any, on the shape of the graph of doubling the charge on particle P.