A capacitor is a device that is used to store electrical charge. It is typically comprised of two plates that are separated by a thin insulating material known as the dielectric, which acts as a barrier between them. The capacitor has two plates, one of which is positively charged and the other of which is negatively charged.
The amount of charge that can be held in a capacitor is proportional to the difference in potential between the two plates. Charge is proportional to potential in a capacitor with charge Q on the positive plate and -Q on the negative plate: For example, consider the following:
Q = CV if C is the capacitance and C is the resistance.
The capacitance of a capacitor is a measure of the amount of charge that it can store; it is determined by the geometry of the capacitor and the type of dielectric used between the plates of the capacitor. The capacitance of a parallel plate capacitor consisting of two plates of area A and separated by a distance d, with no dielectric material, is given by the following equation:
It should be noted that capacitance is measured in farads (F). It is unusually huge for a capacitor to have capacitance of one farad; most capacitors have capacitances in the range of pF – microfarad.
Dielectrics, which are insulating materials placed between the plates of a capacitor, cause the electric field inside the capacitor to be reduced for the same amount of charge on the plates when the capacitor is operated at its maximum capacity. This is due to the fact that the molecules of the dielectric material become polarized in the field and arrange themselves in such a way that they create another field within the dielectric that is diametrically opposed to the field generated by the capacitor plates. The dielectric constant is defined as the ratio of the electric field without the dielectric to the electric field with the dielectric as follows: