(a)[2]
Define what electric potential at a point means.
(b(i))[1]
In an $\alpha$-particle scattering experiment, $\alpha$-particles are aimed at a thin gold foil, as shown in Fig. 9.1. The apparatus is in a vacuum. The gold-197 ($^{197}_{79}\text{Au}$) nuclei in the foil may be treated as fixed point charges. Each $\alpha$-particle emitted by the source has an energy of $4.8\,\text{MeV}$. Calculate the initial kinetic energy $E_K$, in joules, of one $\alpha$-particle from the source.
(b(ii))[4]
Calculate the distance $d$ at the closest approach of an $\alpha$-particle to a gold nucleus.
(c)[1]
Use your answer in (b)(ii) to comment on what the diameter of a gold nucleus might be.