Capacitor

This article is about the electronic component. For the physical phenomenon, see Capacitance. For an overview of types, see Capacitor types.
"Capacitive" redirects here. For the term used when referring to touchscreens, see Capacitive sensing.

Capacitor
TypeElectronic component
Working principle‍Capacitance
InventedEwald Georg von Kleist (1745)
Pieter van Musschenbroek (1746)
Electronic symbol

In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser,[1] a term still encountered in a few compound names, such as the condenser microphone. It is a passive electronic component with two terminals.

The utility of a capacitor depends on its capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed specifically to add capacitance to some part of the circuit.

The physical form and construction of practical capacitors vary widely and many types of capacitor are in common use. Most capacitors contain at least two electrical conductors, often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, air, and oxide layers. When an electric potential difference (a voltage) is applied across the terminals of a capacitor, for example when a capacitor is connected across a battery, an electric field develops across the dielectric, causing a net positive charge to collect on one plate and net negative charge to collect on the other plate. No current actually flows through a perfect dielectric. However, there is a flow of charge through the source circuit. If the condition is maintained sufficiently long, the current through the source circuit ceases. If a time-varying voltage is applied across the leads of the capacitor, the source experiences an ongoing current due to the charging and discharging cycles of the capacitor.

Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy, although real-life capacitors do dissipate a small amount (see Non-ideal behavior).

The earliest forms of capacitors were created in the 1740s, when European experimenters discovered that electric charge could be stored in water-filled glass jars that came to be known as Leyden jars. Today, capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow.[2] The property of energy storage in capacitors was exploited as dynamic memory in early digital computers,[3] and still is in modern DRAM.

  1. ^ Duff, Wilmer (1916) [1908]. A Text-Book of Physics (4th ed.). Philadelphia: P. Blakiston's Son & Co. p. 361. Retrieved 2016-12-01.
  2. ^ Bird, John (2010). Electrical and Electronic Principles and Technology. Routledge. pp. 63–76. ISBN 978-0-08089056-2. Retrieved 2013-03-17.
  3. ^ Floyd, Thomas (2005) [1984]. Electronic Devices (7th ed.). Upper Saddle River, New Jersey, USA: Pearson Education. p. 10. ISBN 0-13-127827-4.