How does one prove that the force between two conductor plates is F=q^2/2eA, where e=epsilon. If I use F=qE. Where the electric field is generated by one of the conducting plates: E=q/eA, then F=q^2/eA. I think what the answer assumes is that the E-field is from a uniform plate (insulator): E=q/2eA. In that case, F=q^2/2eA, which is the correct answer. But how can you make that assumption when obviously two conductor plates will have all their charge on the surface facing the other plate?