# 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 capacitor has three essential parts:

• two electrical conductors - usually metal plates
• dielectric - this is the third part that separates and insulates the plates

The plates are charged with equal amounts of positive and negative electrical charges, respectively. This is a physical storage of electricity as compared with the chemical storage in a battery.

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 εr their capacitance, C

Circular solid cylinder (radius a and length l)

Cube (each side of length a)