Capacitance is an electrical effect that opposes change in voltage between conducting surfaces separated by an insulator. Capacitance stores electrical energy when electrons are attracted to nearby but separate surfaces. The voltage across an unchanging capacitance value will stay constant unless the quantity of charge stored is changed.

The unit of capacitance is the Farad, in honor of Michael Faraday's work with electrostatics. When a 1-Farad capacitance stores 1 Coulomb the result will be 1 volt. The Coulomb is the basic unit of electrical charge, equal to 6.2422 x 10 18 charges the size carried by an electron or by a proton.

An electrical component that introduces capacitance is called a capacitor. Practical capacitors may have as small a value as a few trillionths of a Farad or as large as several Farads.

Work is performed to accumulate charge in a capacitor. Each additional electron stored must overcome the repelling force caused by...