Editing Farad (section)

==Explanation==
[[File:Capacitors Various.jpg|thumb|Examples of different types of capacitors]]
A [[capacitor]] generally consists of two conducting surfaces, frequently referred to as plates, separated by an insulating layer usually referred to as a [[dielectric]]. The original capacitor was the [[Leyden jar]] developed in the 18th century. It is the accumulation of electric charge on the plates that results in [[capacitance]]. Modern capacitors are constructed using a range of manufacturing techniques and materials to provide the extraordinarily wide range of capacitance values used in [[electronics]] applications from femtofarads to farads, with maximum-voltage ratings ranging from a few [[volt]]s to several kilovolts.

Values of capacitors are usually specified in terms of [[SI prefix#List of SI prefixes|SI prefixes]] of farads (F), <!--'''millifarads''' (mF),--> '''microfarads''' ('''μF'''), '''nanofarads''' ('''nF''') and '''picofarads''' ('''pF''').<ref name="Braga">{{cite book |title=Robotics, Mechatronics, and Artificial Intelligence |last=Braga |first=Newton C. |year=2002 |access-date=2008-09-17 |publisher=Newnes |page=21 |url=https://books.google.com/books?id=yqb-f-HKem0C&q=microfarad+common+measurement&pg=PA21 |isbn=0-7506-7389-3 |quote=Common measurement units are the microfarad (μF), representing 0.000,001 F; the nanofarad (nF), representing 0.000,000,001 F; and the picofarad (pF), representing 0.000,000,000,001 F.}}</ref> The '''millifarad''' ('''mF''') is rarely used in practice; a capacitance of 4.7&nbsp;mF (0.0047&nbsp;F), for example, is instead written as {{gaps|4|700|u=μF}}. The '''nanofarad''' ('''nF''') is used more often in Europe than in the United States.<ref>{{cite book |title=Make: Electronics: Learning Through Discovery |last=Platt |first=Charles |year=2009 |access-date=2014-07-22 |publisher=O'Reilly Media |page=61 |url=https://books.google.com/books?id=PQzYdC3BtQkC&q=nanofarad&pg=PA61 |isbn=9781449388799 |quote=Nanofarads are also used, more often in Europe than in the United States.}}</ref> The size of commercially available capacitors ranges from around 0.1&nbsp;pF to {{gaps|5|000|F}} (5&nbsp;kF) [[supercapacitor]]s. [[Parasitic capacitance]] in high-performance [[integrated circuit]]s can be measured in femtofarads (1 fF = 0.001&nbsp;pF = {{10^|-15}}&nbsp;F), while high-performance test equipment can detect changes in capacitance on the order of tens of attofarads (1&nbsp;aF = {{10^|−18}}&nbsp;F).<ref>{{cite book |title=Analog MOS Integrated Circuits for Signal Processing |last=Gregorian |first=Roubik |year=1976 |publisher=John Wiley & Sons |page=78}}</ref>

A value of 0.1&nbsp;pF is about the smallest available in capacitors for general use in electronic design, since smaller ones would be dominated by the [[parasitic capacitance]]s of other components, wiring or [[printed circuit board]]s. Capacitance values of 1&nbsp;pF or lower can be achieved by twisting two short lengths of insulated wire together.<ref>{{cite web |title=What's All This Femtoampere Stuff, Anyhow? |url=https://www.electronicdesign.com/test-amp-measurement/whats-all-femtoampere-stuff-anyhow |last=Pease |first=Bob |author-link=Bob Pease |publisher=Electronic Design |date=2 September 1993 |access-date=2013-03-09}}</ref><ref>{{cite web |title=What's All This Best Stuff, Anyhow? |url=https://www.electronicdesign.com/analog/whats-all-best-stuff-anyhow |last=Pease |first=Bob |publisher=Electronic Design |date=1 December 2006 |access-date=2013-03-09}}</ref>

The capacitance of the Earth's [[ionosphere]] with respect to the ground is calculated to be about 1&nbsp;F.<ref>{{cite web |url=http://konfluence.org/efield.pdf |title=Electrical Properties of the Fair-Weather Atmosphere and the Possibility of Observable Discharge on Moving Objects |last=Williams |first=L. L. |date=January 1999 |access-date=2012-08-13 |archive-url=https://web.archive.org/web/20161221015744/http://konfluence.org/efield.pdf |archive-date=2016-12-21 |url-status=dead }}</ref>

===Informal and deprecated terminology===
The picofarad (pF) is sometimes colloquially pronounced as "puff" or "pic", as in "a ten-puff capacitor".<ref>{{cite web |title=Puff |url=http://scienceworld.wolfram.com/physics/Puff.html |publisher=Wolfram Research |access-date=2009-06-09}}</ref> Similarly, "mic" (pronounced "mike") is sometimes used informally to signify microfarads.

Nonstandard abbreviations were and are often used. Farad has been abbreviated "f", "fd", and "Fd". For the prefix "micro-", when [[mu (letter)|the Greek small letter "μ"]] or the legacy micro sign "μ" is not available (as on typewriters) or inconvenient to enter, it is often substituted with the similar-appearing "u" or "U", with little risk of confusion. It was also substituted with the similar-sounding "M" or "m", which can be confusing because M officially stands for 1,000,000, and m preferably stands for 1/1000. In texts prior to 1960, and on capacitor packages until more recently, "microfarad(s)" was abbreviated "mf" or "MFD" rather than the modern "μF". A 1940 [[Radio Shack]] catalog listed every capacitor's rating in "Mfd.", from 0.000005 Mfd. (5 pF) to 50 Mfd. (50 μF).<ref>{{cite web |title=1940 Radio Shack Catalog - Page 54 - Condensers |url=http://www.radioshackcatalogs.com/html/1940/hr054.html |website=radioshackcatalogs.com |access-date=11 July 2017 |archive-url=https://web.archive.org/web/20170711160428/http://www.radioshackcatalogs.com/html/1940/hr054.html |archive-date=11 July 2017}}</ref>

"Micromicrofarad" or "micro-microfarad" is an obsolete unit found in some older texts and labels, contains a nonstandard [[metric double prefix]]. It is exactly equivalent to a picofarad (pF). It is abbreviated μμF, uuF, or (confusingly) "mmf", "MMF", or "MMFD".

Summary of obsolete or deprecated capacitance units or abbreviations: (upper/lower case variations are not shown)
* μF (microfarad) = mf, mfd, uf
* pF (picofarad) = mmf, mmfd, pfd, μμF

{{unichar|3332}} is a square version of {{lang|ja|ファラッド}} ({{Transliteration|ja|faraddo}}, the Japanese word for "farad") intended for Japanese [[vertical text]]. 
It is included in Unicode for [[CJK Compatibility|compatibility with earlier character sets]].

===Related concepts===
The reciprocal of capacitance is called [[elastance|electrical elastance]], the (non-standard, non-SI) unit of which is the [[daraf]].<ref>{{cite web|title=Daraf |url=http://www.websters-dictionary-online.com/definitions/daraf |publisher=Webster's Online Dictionary |access-date=2009-06-19 |url-status=dead |archive-url=https://web.archive.org/web/20111004054525/http://www.websters-dictionary-online.com/definitions/daraf |archive-date=2011-10-04 }}</ref>