A capacitor is another way to store electric energy. It is kind of like a battery, but batteries store potential energy in the form of chemical energy, which is then converted to electric energy upon use. Capacitors, on the other hand, store energy inside an electric field to be called on and used later.
A capacitor has two sides, a positive side and a negative side, separated by an insulting material (dielectric) that ensures that charges on one side cannot touch those on the other side. Because the positive side is attracted to the negative side, an electric field forms within the capacitor— this is where the potential is stored.
Charges are pushed into each side and stay there unless a path opens up for them. If the capacitor is disconnected from a power source, the field will remain until all of the charges have left through paths being opened for them. This provides a source of power in case of outages or alternating currents, creating a stable current.
Capacitance (C) is measured in Farads (), or . , and the potential energy of a capacitor is equal to . Also see the electricity formula sheet.