Principle and Working:
The relation between capacitance C, charge Q and charging voltage E is given as C=Q/E. The capacitance of a parallel plate capacitor depends upon the distance d between the plates, area A of the plates and the nonconductive material (having dielectric constant er) between the plates. Thus capacitance is
C = er e0 A/d
Where e0 = 8.85 x 10-12 As/Vm (permittivity in free space),
...
In present setup, the parallel plate are charged by 0-400 V DC power supply. The charge Q on the parallel plate is measured by electrometer amplifier as voltage. The distance between plate is adjusted by placing spacer on the edges of plate.