A capacitor is a device for storing charge. The simplest type of capacitor is made up of two conductors separated by either empty space or by an insulating material known as the dielectric. One conductor of the capacitor is positively charged, while the other has negative charge.

The amount of charge a capacitor can store for a given potential difference is measured by its capacitance, C. The unit of capacitance is the farad (F).

The charge stored in a capacitor is proportional to the potential difference between the two conductors. For a capacitor with a charge of +Q on one plate and -Q on the other:

Q = C DV