Question: how to calculate potential difference across a parallel plate capacitor?
Answer: Thus, the potential difference between the plates of both capacitors is VA - VB = Vbat. We have C1 = Q1/Vbat and C2 = Q2/Vbat, where Q1 is the charge on capacitor C1, and Q2 is the charge on capacitor C2. Let C be the equivalent capacitance of the two capacitors in parallel, i.e. C = Q/Vbat, where Q = Q1 + Q2.