Question

a parallel plate capacitor has an area of 5cm^2 and a capacitance of 3.5PF. the capacitor is connected to a 12v battery .after the capacitor is completely charge up the battery is removed.
a)what must be the separation of the plates and the charge density on the plate
b)what is the magnitude of the electric field between the plate and how much energy is stored in the electric field between the plates
c)if a sheet of mylar is placed between the plates how will the voltage across the plate and the charge density on the plate change?
d)if the sheet of mylar has an area of 3cm^2 so that it doesn't cover the whole area of the plate what would be the effective capacitance of this arrangement

Answer 1

d = epsilon A/C
E = V/d (E field)
E = 1/2CV^2 (Energy)
Don't know the kappa for mylar but
C = kappa epsilon A/d

Answer 2

if the mylar is removed and the plates are moved 1mm further from each other what will be the voltage across the plate and how much work will it take to move the plate apart