As many of you may know, a capacitor stores energy by means of the electric field crested between the plates of this capacitor, but how is the electric field able to store the energy itself?
The energy stored in a capacitor is created when charges are separated, i.e., electrons are separated from atoms on one plate and, effectively, moved to the other plate.
I say, effectively, because the electrons arriving to the other plate are not literally the same electrons that were removed from the first plate, but, from the energy standpoint, it does not make a difference.
Again, although a physical path of the electrons apparently goes through a battery (or another energy sources), the effect is the same as if the electrons were taken from one plate and moved directly to the other plate (through the gap, if you will), against the attraction forces of positive ions left behind. This process is analogous to the stretch of a spring: it converts chemical energy of a battery into electrostatic energy of the capacitor.
If the battery is replaced by a wire, the separated electrons would flow back and reunite with the positive ions, converting the electrostatic energy to heat. This process of energy release is analogous to the contraction of a stretched spring.
The field cause charges to be induced in the gap between plates which will increase or decrease the capacitance of the capacitor depending on the material between the plates.
Capacitance = k(dielectric constant)(A)/(d) Dielectric constant may also be called permittivity Vacuum = 1 C^2/Nm^2 Air = 1.00054 Paper = 3.5 Rubber = 7