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
AIPMT 2015, Medium
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Force of attraction between the plates of the parallel plate air capacitor is
$F=\frac{Q^{2}}{2 \varepsilon_{0} A}$
where $Q$ is the charge on the capacitor, $\varepsilon_{0}$ is the permittivity of freespace and $A$ is the area of each plate.
But $Q=C V$
and $C=\frac{\varepsilon_{0} A}{d}$ or $\varepsilon_{0} A=C d \quad \therefore \quad F=\frac{C^{2} V^{2}}{2 C d}=\frac{C V^{2}}{2 d}$
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