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Glossary of Capacitor Terms

Illinois Capacitor provides this list of capacitor terminology to assist our customers, students and educators alike.  If you have a comment on a definition, or have a suggestion for additions, please let us know.

Aluminum Electrolytic Capacitor

A capacitor made up of two aluminum electrodes seperated by paper saturated with an electrolyte. The dielectric is the oxide of the anode.


The positive electrode of an electrolytic capacitor.


A situation where Direct Current (DC) is kept from a circuit element due to the high series impedence of a capacitor.

By-passing (De-Coupling)

A situation where the AC portion of a signal is kept from a circuit element via a low impedence path in parallel with the circuit element.


A measure of the energy storage capability of a capacitor at a given voltage usually expressed in farads, microfarads, nanofarads, or picofarads.

Capacitive Reactance (Xc)

The opposition to the flow of alternating or pulsating current by a capacitor measured in ohms. The imaginery component of the impedence of a capacitor.

Capacitive Reactance Formula


A passive circuit element capable of storing electrical energy and releasing it at a predetermined time and at a predetermined rate.


The negative electrode of a capacitor.


The quantity of electrical charge measured in coulombs.


Situation where two circuits are connected together where only the AC voltage is passed.


The amount of charge moving past a given reference point over time.


An insulating or non-conductive medium between the plates of a capacitor.

Dielectric Absorption

A measure of the reluctance of a capacitor's dielectric to discharge completely - usually measured in percent of original charge.

Dielectric Constant

The ratio of a capacitor's capacitance with a given dielectric to the same capacitor having a vacuum as a dielectric.

Dissipation Factor (D.F. or Tan delta)

A measure of the losses in a capacitor expressed as the ratio of the E.S.R. of a capacitor to its reactance at a specific frequency and temperature.

dv/dt Rating

The maximum voltage rise (or discharge) time a capacitor can withstand being damaged.


See supercapacitors


A current-conducting solution between the electrodes of a capacitor used to replenish the dielectric in an aluminum electrolytic capacitor.

Equivalent Series Resistance (E.S.R.)

The sum of all the internal resistances of a capacitor measured in ohms. Expressed mathematically as ESR = D.F.*Xc.


The basic unit of a measure of a capacitor. A capacitor charged to 1 volt with a charge of 1 coulomb would have a capacitance of 1 farad. 1 microF = .000001 Farads.

Film Capacitors

A capacitor made up of two metal plates seperated by a plastic(polymer) dielectric material.


The rate at which an alternating or pulsating wave repeats itself expressed in cycles per second (C.P.S.) or hertz (Hz).

Impedance (Zc)

The total opposition offered to alternating or pulsating current measured in ohms. Impedence is the vector sum of the resistive and reactive components of a capacitor expressed mathematically as

Impedance Formula

Insulation resistance

The ratio of the DC voltage applied to the terminals of a capacitor and the resultant leakage current flowing through the dielectric and over its surface after the initial charging current has ceased expressed in megohms or as time constant megohm x microfarads.

Leakage Current

Measure of the stray direct current flowing through capacitor after DC voltage is impressed on it.

Metallized Capacitor

A capacitor where a thin layer of metal is vacuum-deposited directly onto the dielectric.

Ripple Current

The total amount of alternating and direct current that can be applied to a capacitor under specific conditions without causing a failure.

Snubber Capacitor

Capacitors used independently or with other circuit elements to suppress voltage transients in electrical circuits.


Supercapacitors also called ultracapacitors or Electric double layer capacitors (EDLC) are capacitors made up of 2 metal plates with a carbon dielectric material and a conductive electrolyte.

Surge Voltage (SV)

The maximum DC voltage a capacitor can tolerate under any circumstances for a short period of time without suffering any damage.


The maximum deviation from a nominal capacitance value at specific conditions expressed as a percentage of nominal capacitance.


The force or electrical pressure which causes current to flow through a conductor.

Ultra Capacitor

See supercapacitors

Working Voltage (WVDC)

The maximum DC voltage applied to a capacitor for continuous operation at maximum rated temperature.