A capacitor is a device that stores electrical energy in an electric field. It is a passive electronic component with two terminals. The basic function of a capacitor is to store energy in the form of an electric field. When connected to a circuit, it can release this stored energy to supply current to the load. Capacitors are widely used in electronic devices such as radios, televisions, computers, and other consumer electronics.
How Capacitors Work
A capacitor consists of two conductors (usually metal plates) separated by an insulating material called a dielectric. When voltage is applied to the conductors, an electric field forms across the dielectric. This field stores energy in the form of potential difference between the conductors. The amount of charge that can be stored on each conductor is proportional to its surface area.
The simplest form of a capacitor is two metal plates separated by air; however, most capacitors use rolled up sheets of paper or plastic as the dielectric material because these materials have a higher dielectric constant than air (meaning they can store more charge for a given voltage).
The value of capacitance (C), measured in Farads (F), depends on four factors:
•the size and shape of the plates
•the distance between them (d)
•the type and permittivity (εr) of the dielectric material between them
mathematically: C= Q/V = εA/d where A =surface area
If both plates have equal and opposite charges (+Q and -Q) then no net charge exists on either plate so there will be no flow of current through the external circuit when voltage is first applied. However, once voltage has been applied and removed again from the circuit there will be some residual charge left on each plate due to unavoidable leakage currents; this results in what is known as ‘capacitor ageing’. In general double layer capacitors have very low leakage currents compared with electrolytic capacitors making them more suited for applications where power must be stored for long periods without refreshing such as backup power supplies or computer memory back-up batteries