A parallel plate capacitor is constructed by placing square metal sheets of side length 30 cm on either side of a sheet of polythene which is 2mm thick
If the permeability of the polythene is 2.2 *10^-11 F m^-1, what is the capacitance of the system
(ii)If a 50V power supply is connected across the plates, calculate the charge on the plates and the energy stored in the capacitor
(iii) If the polythene is withdrawn from the capacitor until only half of the space bewtween the plates is occupied by it, what is the charge on the plates and the energy stored in this case?
The Attempt at a Solution
I think i could do part 1 and 2 alright just using the standard equations
(i)C = (2.2*10^-11)*(9.o*10^-2)/(2.0*10^-3) = 9.9*10^-10
Q= (9.9*10^-10)*50 = 4.95*10^-8
E = 0.5(9.9*10^-10)*(50^2)= 1.24*10^-6
(iii)I dont know what to do for this part, Will the voltage decrease and the charge also?
any tips or hints would be very much appreciated