A parallel plate air capacitor has capacity C, distance of separation between plates is d and potential difference V is applied between the plates. Force of attraction between the plates of the parallel plate air capacitor is

 Force of attraction between the plates of the parallel plate air capacitor is

$\mathrm{F}=\frac{{\mathrm{Q}}^2}{2{\mathrm{\epsilon }}_0\mathrm{A}}$

where Q is the charge on the capacitor, ${\epsilon }_0$ is the permittivity of free space and A is the area of each plate.

$\text{ But }\mathrm{Q}=\mathrm{CV}$

$\text{ and }\mathrm{C}=\frac{{\mathrm{\epsilon }}_0\mathrm{A}}{\mathrm{d}}\text{ or }{\mathrm{\epsilon }}_0\mathrm{A}=\mathrm{Cd} \therefore \mathrm{F}=\frac{{\mathrm{C}}^2{\mathrm{V}}^2}{2\mathrm{Cd}}=\frac{{\mathrm{CV}}^2}{2\mathrm{d}}$