A one farad modern super-capacitor. The scale behind is in inches (top) and centimetres (bottom).
|Unit system||SI derived unit|
|Named after||Michael Faraday|
|In SI base units:||s4⋅A2⋅m−2⋅kg−1|
One farad is defined as the capacitance across which, when charged with one coulomb, there is a potential difference of one volt. Equally, one farad can be described as the capacitance which stores a one-coulomb charge across a potential difference of one volt.
The relationship between capacitance, charge, and potential difference is linear. For example, if the potential difference across a capacitor is halved, the quantity of charge stored by that capacitor will also be halved.
For most applications, the farad is an impractically large unit of capacitance. Most electrical and electronic applications are covered by the following SI prefixes:
It can further be expressed as:
The term "farad" was originally coined by Latimer Clark and Charles Bright in 1861, in honor of Michael Faraday, for a unit of quantity of charge, but by 1873, the farad had become a unit of capacitance. In 1881 at the International Congress of Electricians in Paris, the name farad was officially used for the unit of electrical capacitance.
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 volts to several kilovolts.
Values of capacitors are usually specified in farads (F), microfarads (μF), nanofarads (nF) and picofarads (pF). The millifarad is rarely used in practice (a capacitance of 4.7 mF (0.0047 F), for example, is instead written as 4700 µF), while the nanofarad is uncommon in North America. The size of commercially available capacitors ranges from around 0.1 pF to 5000F (5 kF) supercapacitors. Parasitic capacitance in high-performance integrated circuits can be measured in femtofarads (1 fF = 0.001 pF = 10−15 F), while high-performance test equipment can detect changes in capacitance on the order of tens of attofarads (1 aF = 10−18 F).
A value of 0.1 pF is about the smallest available in capacitors for general use in electronic design, since smaller ones would be dominated by the parasitic capacitances of other components, wiring or printed circuit boards. Capacitance values of 1 pF or lower can be achieved by twisting two short lengths of insulated wire together.
The picofarad (pF) is sometimes colloquially pronounced as "puff" or "pic", as in "a ten-puff capacitor". 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 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 1000000 (or 1000), 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).
"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".
The statfarad (abbreviated statF) is a rarely used CGS unit equivalent to the capacitance of a capacitor with a charge of 1 statcoulomb across a potential difference of 1 statvolt. It is 1/(10−5c2) farad, approximately 1.1126 picofarads.
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.
Nanofarads are also used, more often in Europe than in the United States.
Abdumuqit Vohidov is a citizen of Tajikistan who was held in extrajudicial detention, for five years, in the United States' Guantanamo Bay detention camps, in Cuba. His Guantanamo Internment Serial Number was 90. Vohidov was returned to his native Tajikistan on 28 February 2007.Capacitance
Capacitance is the ratio of the change in an electric charge in a system to the corresponding change in its electric potential. There are two closely related notions of capacitance: self capacitance and mutual capacitance. Any object that can be electrically charged exhibits self capacitance. A material with a large self capacitance holds more electric charge at a given voltage than one with low capacitance. The notion of mutual capacitance is particularly important for understanding the operations of the capacitor, one of the three elementary linear electronic components (along with resistors and inductors).
The capacitance is a function only of the geometry of the design (e.g. area of the plates and the distance between them) and the permittivity of the dielectric material between the plates of the capacitor. For many dielectric materials, the permittivity and thus the capacitance, is independent of the potential difference between the conductors and the total charge on them.
The SI unit of capacitance is the farad (symbol: F), named after the English physicist Michael Faraday. A 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates. The reciprocal of capacitance is called elastance.Capacitive power supply
A capacitive power supply, also called a capacitive dropper, is a type of power supply that uses the capacitive reactance of a capacitor to reduce the mains voltage to a lower voltage. There are two important limitations: First, the high withstanding voltage required of the capacitor, along with the high-capacitance required for a given output current, mean that this type of supply is only practical for low-power applications. (The capacitance needed increases with the current to be drawn; high capacitance mains-voltage capacitors are expensive and bulky.) The second is that due to the absence of electrical isolation between input and output, anything connected to the power supply must be reliably insulated so that it is not possible for a person to come into electrical contact with it. By the equation of state for capacitance, where , the current is limited to: 1 amp, per farad, per volt-rms, per radian (of phase). Or amps, per farad, per volt-rms, per hertz.Coulomb
The coulomb (symbol: C) is the International System of Units (SI) unit of electric charge. It is the charge (symbol: Q or q) transported by a constant current of one ampere in one second:
Thus, it is also the amount of excess charge on a capacitor of one farad charged to a potential difference of one volt:
The coulomb is equivalent to the charge of approximately 6.242×1018 (1.036×10−5 mol) protons, and −1 C is equivalent to the charge of approximately 6.242×1018 electrons.
A new definition, in terms of the elementary charge, took effect on 20 May 2019. The new definition defines the elementary charge (the charge of the proton) as exactly 1.602176634×10−19 coulombs.Elastance
Electrical elastance is the inverse of capacitance. The SI unit of elastance is the inverse farad (F−1). The concept is not widely used by electrical and electronic engineers. The value of capacitors is invariably specified in units of capacitance rather than inverse capacitance. However, it is used in theoretical work in network analysis and has some niche applications at microwave frequencies.
The term elastance was coined by Oliver Heaviside through the analogy of a capacitor as a spring. The term is also used for analogous quantities in some other energy domains. It maps to stiffness in the mechanical domain, and is the inverse of compliance in the fluid flow domain, especially in physiology. It is also the name of the generalised quantity in bond-graph analysis and other schemes analysing systems across multiple domains.Emmanuel Iduma
Emmanuel Iduma (born 1989) is a Nigerian writer, editor, publisher, and art critic. He is the co-founder of Saraba Magazine and the author of The Sound of Things to Come (2012). He teaches in the MFA Art Writing Program at School of Visual Arts, New York City.Farad, California
Farad is a former settlement in Nevada County, California. Farad is located on the Southern Pacific Railroad, 1 mile (1.6 km) south-southwest of Mystic. The Truckee River crosses Farad halfway between Truckee, CA and Reno, NV.The Farad Hydroelectric Plant was built alongside the Truckee River at 39.4196304°N 120.0318647°W / 39.4196304; -120.0318647 by the Sierra Pacific Power Company in 1899.Farad (disambiguation)
The farad (symbol: F) is an SI derived unit of electrical capacitance.
Farad or FARAD may also refer to:
Farád, a village in Hungary
Farad, California, a former settlement in United States
Farad Azima, British industrialist, technology entrepreneur and philanthropist
FARAD, the Faraday Accelerator with Radio-frequency Assisted DischargeFarad Azima
Farad Azima is an Industrialist, technology entrepreneur and philanthropist. His postgraduate studies were at Leeds University until 1972, where he is an active alumnus. He has numerous international Patents in diverse areas of engineering.Farád
Farád is a village in Győr-Moson-Sopron county, Hungary.Jar (unit)
A jar was an early unit of capacitance once used by the British Royal Navy. The term originated as the capacitance of a Leyden jar. Its value is such that one farad is 9×108 jars and one jar is 1111 picofarads.Journal of the Chemical Society, Faraday Transactions
The Journal of the Chemical Society, Faraday Transactions was a peer-reviewed scientific journal published from 1905 until 1998. The journal was originally published by the Faraday Society under the name Transactions of the Faraday Society and was renamed in 1972.Lamentations of Mary
The Old Hungarian Lamentations of Mary (OHLM) (Hungarian: Ómagyar Mária-siralom) is the oldest extant Hungarian poem. It was copied in c. 1300 into a Latin codex, similarly to the first coherent Hungarian text, the Halotti beszéd (Funeral Oration), which was written between 1192 and 1195. Its text is a translation or adaptation of a version of the poem, or rather "sequence", that begins Planctus ante nescia and that was very widespread in medieval Europe. The speaker of the poem is the Blessed Virgin Mary as she laments the crucifixion of her Son, Jesus Christ while being at the side of His Cross on Calvary. As such the poem constitutes an element of Roman Catholic religious poetry. Its interpretation has been much discussed in Hungarian philology, and the meaning of some words and phrases remains disputed. Pais Dezső's interpretation is given herein, but it also relies on earlier relevant results.Permittivity
In electromagnetism, absolute permittivity, often simply called permittivity, usually denoted by the Greek letter ε (epsilon), is the measure of capacitance that is encountered when forming an electric field in a particular medium. More specifically, permittivity describes the amount of charge needed to generate one unit of electric flux in a particular medium. Accordingly, a charge will yield more electric flux in a medium with low permittivity than in a medium with high permittivity. Permittivity is the measure of a material's ability to store an electric field in the polarization of the medium.
The SI unit for permittivity is farad per meter (F/m or F·m−1).
The lowest possible permittivity is that of a vacuum. Vacuum permittivity, sometimes called the electric constant, is represented by ε0 and has a value of approximately 8.85×10−12 F/m.
The permittivity of a dielectric medium is often represented by the ratio of its absolute permittivity to the electric constant. This dimensionless quantity is called the medium’s relative permittivity, sometimes also called "permittivity". Relative permittivity is also commonly referred to as the dielectric constant, a term which has been deprecated in physics and engineering as well as in chemistry.
By definition, a perfect vacuum has a relative permittivity of exactly 1. The difference in permittivity between a vacuum and air can often be considered negligible, as κair = 1.0006.
Relative permittivity is directly related to electric susceptibility (χ), which is a measure of how easily a dielectric polarizes in response to an electric field, given by
otherwise written as
A pulsed inductive thruster (PIT) is a form of ion thruster, used in spacecraft propulsion. It is a plasma propulsion engine using perpendicular electric and magnetic fields to accelerate a propellant with no electrode.Uomini più uomini
Uomini più uomini (Italian for Men More Men) is the eighth studio album by French singer Amanda Lear, released in 1989 by Ricordi International.Volt
The volt (symbol: V) is the derived unit for electric potential, electric potential difference (voltage), and electromotive force. It is named after the Italian physicist Alessandro Volta (1745–1827).Wallace Fard Muhammad
Wallace D. Fard, also known as Wallace Fard Muhammad (; reportedly born February 26, c. 1877 – circa 1934), was the founder of the Nation of Islam. He arrived in Detroit in 1930 with an obscure background and several aliases, and taught an idiosyncratic form of Islam to members of the city's black population. In 1934 he disappeared from public record, and Elijah Muhammad succeeded him as leader of the Nation of Islam.
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