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# The Online Encyclopedia and Dictionary   ## Encyclopedia ## Dictionary ## Quotes  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: $\mbox{C}\cdot \mbox{V}^{-1} = \mbox{m}^{-2}\cdot \mbox{kg}^{-1}\cdot \mbox{s}^4\cdot \mbox{A}^2$

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The farad should not be confused with the faraday, an old unit of charge nowadays superseded by the coulomb.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 Electrical elastance, the (non-standard, non-SI) unit of which is the daraf.

## SI electricity units  