Question
Two parallel-plate capacitors X and Y have the same area of plates and same separation between them. X has air between the plates, while Y contains a dielectric medium of 
i) Calculate capacitance of each capacitor if the equivalent capacitance of the combination is 4 
ii) Calculate the potential difference between the plates x and Y
iii) Estimate the ratio of electrostatic energies stored in x and Y
Solution
i)
Capacitance of a parallel plate capacitor is given by, 
ii)
Potential difference between plates X and Y can be calculated as,
Q = CV 
iii)
The ratio of electrostatic energies can be calculated as: 
