Farad Farad

Farad - Definition and Overview

The farad (symbol F) is the SI unit of capacitance (named after Michael Faraday). A capacitor has a value of one farad when one coulomb of charge causes a potential difference of one volt across it. Its equivalent expressions in other SI units are:

<math>\mbox{C}\cdot \mbox{V}^{-1} = \mbox{m}^{-2}\cdot \mbox{kg}^{-1}\cdot \mbox{s}^4\cdot \mbox{A}^2<math>

Since the farad is a very large unit, values of capacitors are usually expressed in microfarads (μF), nanofarads (nF), or picofarads (pF). Multiples higher than the microfarad are rarely used in practice, even for large capacitances, so that a capacitance of 4.7×10-3 F, for example, is usually written as 4700 μF.

The farad should not be confused with the faraday, an old unit of charge nowadays superseded by the coulomb.

The reciprocal of capacitance is called elastance, the (non-standard, non-SI) unit of which is the daraf.

SI electricity units

SI electromagnetism units

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Name Symbol Dimensions Quantity
ampere (SI base unit) A A Current
coulomb C A·s Electric charge, Quantity of electricity
volt V J/C = kg·m2·s−3·A−1 Potential difference
ohm Ω V/A = kg·m2·s−3·A−2 Resistance, Impedance, Reactance
ohm metre Ω·m kg·m3·s−3·A−2 Resistivity
farad F C/V = kg−1·m−2·A2·s4 Capacitance
farad per metre F/m kg−1·m−3·A2·s4 Permittivity
reciprocal farad F−1 kg1·m2·A−2·s−4 Elastance
siemens S Ω−1 = kg−1·m−2·s3·A2 Conductance, Admittance, Susceptance
siemens per metre S/m kg−1·m−3·s3·A2 Conductivity
weber Wb V·s = kg·m2·s−2·A−1 Magnetic flux
tesla T Wb/m2 = kg·s−2·A−1 Magnetic flux density
ampere per metre A/m m−1·A magnetic induction
ampere-turns per weber A/Wb kg−1·m−2·s2·A2 Reluctance
henry H V·s/A = kg·m2·s−2·A−2 Inductance
henry per metre H/m kg·m·s−2·A−2 Permeability
(dimensionless) - - Magnetic susceptibility


Example Usage of Farad
GommeBlog: Farad Snow, catene da neve per auto non catenabili e tante misure di pneumatici http://ff.im/bN6Mt
pegazoo: Szerintem nem a rest Farad ketszer, hanem az aki miattuk dolgozik.
dickerone: SAVE $68.17 - Boss CAP3.5R 3.5 Farad Capacitor (Red) $43.83 http://dealnay.com/135871 #amplifier #discount
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