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Question:

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:

C2V22d

C2Vd

C2V22d2

CV22d

Solution:

Force of attraction between the plates is
F=Q22Aε0
or
F=C2V22Aε0
where Q=CV
also C=Aε0d ⇒ Aε0=Cd
now, F=C2V22Cd=CV22d