(a(i))[2]
State Coulomb’s law for point charges.
(a(ii))[2]
Treat the $\alpha$-particle and the proton as point charges. Calculate the electric force between the $\alpha$-particle and the proton.
(b(i))[2]
Define electric field strength in terms of force per unit charge.
(b(ii).1)[2]
Explain why the two separate electric fields carry opposite signs.
(b(ii).2)[3]
On Fig. 4.2, sketch how the combined electric field due to the $\alpha$-particle and the proton varies with $x$ for values of $x$ from $4\ \mu\text{m}$ to $16\ \mu\text{m}$.