In a sodium chloride molecule the equilibrium separation of the Na+ and the Cl- ions is 0.24 nm. Assuming that the ions may be considered to be point charges of +q and -q respectively and that the force of attraction between them is 4.1×10-9 N.
(a) Estimate the magnitude of the charge q
(b) Estimate the electric field strength (in magnitude and direction) at the mid-point of the molecule.