Capacitor

A capacitor is a device that stores elecrical charges. A capacitor consists of two conductive plates at different electrical potentials, and an insulating dielectric or insulator. The size of the charge that a particular capacitor can hold is:

 C = Eo * K * L * W / D

where C is the capacitance in Farad?s, E_o is the electrostatic permittivity of vacuum or free space, K is the value of the dielectric or insulator used, and L, W, and D are the length and width of the common surface, and the distance between the plates.

For electronic devices such as radios, the frequency tuning is a combination of capacitance and inductance in the formula:

 1/ frequency = wavelength = C * I

In semiconductor [intergrated circuit]? devices these capacitors are made up of metal lines and insulators on a substrate. They will store charges such as a HIGH or a LOW. For this reason, dynamic RAM (DRAM) was developed which stores bits in periodically-refreshed capacitors.

Capacitors block DC, but allow AC to pass through. The amount of "resistance" of a capacitor to AC is known as capacitive reactance, and varies depending on the AC frequency. Capacitive reactance is given by this formula:

Xc = 1 / (2 * pi * f * C)

where:

• Xc = capacitive reactance, measured in ohms
• f = frequency of AC in hertz
• C = capacitance in farads

Capacitive reactance is the negative imaginary component of impedence?.

see also electricity