Given, the charge stored by the capacitor is Q and voltage is V. Let the capacitance of the capacitor is C.
The capacitance of a parallel plate capacitor is given by,
ε0 is the permittivity of free space,
d is the distance between the plates of the capacitor,
A is the area of the plates
If we double the area and distance between the plates, then the capacitance will become like the equation given below,
⇒ C = ε02A/2d
⇒ C = ε0A/d
The above equation shows that there will be no effect on the capacitance of the parallel plate capacitor.
If C is constant and Q is constant, V will also be constant. By the formula, E = V/d
We can say that Electric field changed.
Hence, Energy density, Ud = 1/2ε0E2 will change.
We have seen that there will be no effect on the capacitance if we double the area and the distance between the plates of the capacitor.