Q.

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            [2015]
 

1 CV2d      
2 C2V22d2      
3 C2V22d      
4 CV22d      

Ans.

(4)

Force of attraction between the plates of the parallel plate air capacitor is F=Q22ε0A

where Q is the charge on the capacitor, ε0 is the permittivity of free space, and A is the area of each plate.

But Q=CV and C=ε0Ad or ε0A=Cd

   F=C2V22Cd=CV22d