Capacitor

An electrical component that passes alternating currents but blocks direct currents. Also called a condenser, it is capable of storing electrical energy or to buffer power supply lines to provide extra charge when needed. Can also be used in other places to filter out sudden changes in voltage. The amount of charge a capacitor can store is measured by it's capacitance. The unit of measurement is the Farad.

The current through a capacitor is defined as:

The energy stored in a capacitor is:

where

I = current through C

C = capacitance

V = potential difference across C

t = time

Q = charge

For conductors in a medium that has a relative permittivity ε_r their capacitance, C

Sphere (radius a)

Circular disk (radius a)

Circular solid cylinder (radius a and length l)

Cube (each side of length a)

Between coaxial cylinders (radius a and radius b where a<b)

Between concentric spheres (radius a and radius b where a<b)

Between parallel cylinders (radius a and seperation 2d)

See also: By-Pass Capacitor, Capacitance, Ceramic Capacitor, Electrolytic Capacitor, Greencap Capacitor, Inductor, Leyden Jar, Varactor.