In an isolated parallel plate capacitor of capacitance C the four surfaces have charges `Q_(1), Q_(2), Q_(3)` and `Q_(4)` as shown in the figure. The potential difference between the plates is :

Explanation

We must be aware that for a given system in isolated state `q_(1)` must be equal to `q_(4)` and these two surfaces will not affect potential difference between the plates. Apart from that we must be aware of the fact that in an electrostatic condition, metal surfaces parallel to such other carry equal and opposite charges on surfaces facing each other hence `q_(2)=-q_(3)`. Potential difference between the plates can be written using q = CV for the capacitor.
`V=(|q_(2)|)/(C )=(|q_(3)|)/(C )`