Farad

Encyclopedia

The

unit of capacitance

. The unit is named after the English physicist Michael Faraday

.

in coulombs which a capacitor

will accept for the potential

across it to change 1 volt

. A coulomb is 1 ampere

second

. Example: A capacitor with capacitance of 47 nF will increase by 1 volt per second with a 47 mA input current.

1 microfarad (μF) = one millionth (10

1 nanofarad (nF) = one billionth (10

1 picofarad (pF) = one trillionth (10

s

It can further be expressed as:

A=ampere

, V=volt

, C=coulomb, J=joule

, m=meter, N=newton, s=second

, W=watt

, kg=kilogram

, Ω=ohm

For electronics, one farad is a fairly large amount of capacitance. The most commonly used submultiples

in electrical and electronic usage are the microfarad, nanofarad and picofarad.

, but it was for a unit of quantity of charge.

The size of commercially available capacitors ranges from around 100 fF (femtofarads, 10

When speaking of capacitor values a

is not available, the notation

The 'farad' should not be confused with the faraday, which is the electric charge carried by one mole

of singly charged ion

s.

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

.

A capacitor 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

s to several kilovolts.

One picofarad is about the smallest value of capacitor available for general use in electronic design, since smaller capacitors would be dominated by the parasitic capacitances (stray capacitance) of other components, wiring or printed circuit board

s. When capacitance values of 1 pF or lower are required, engineers sometimes create their own capacitors by twisting two short lengths of insulated wire together.

The capacitance of the Earth's ionosphere

with respect to the ground is calculated to be about 1.8 F.

). This very large unit is used in medical terminology only.

The

**farad**is the SISi

Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...

unit of capacitance

Capacitance

In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...

. The unit is named after the English physicist Michael Faraday

Michael Faraday

Michael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....

.

## Definition

A farad is the chargeElectric charge

Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...

in coulombs which a capacitor

Capacitor

A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

will accept for the potential

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

across it to change 1 volt

Volt

The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...

. A coulomb is 1 ampere

Ampere

The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...

second

Second

The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

. Example: A capacitor with capacitance of 47 nF will increase by 1 volt per second with a 47 mA input current.

1 microfarad (μF) = one millionth (10

^{-6}) of a farad, or 1,000,000 pF, or 1,000 nF;1 nanofarad (nF) = one billionth (10

^{-9}) of a farad, or 1,000 pF;1 picofarad (pF) = one trillionth (10

^{-12}) of a farad.### Equalities

A farad has the base SI representation of:s

Second

The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

^{4}× AAmpere

The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...

^{2}× m^{-2}× kgKilogram

The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

^{-1}It can further be expressed as:

A=ampere

Ampere

The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...

, V=volt

Volt

The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...

, C=coulomb, J=joule

Joule

The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

, m=meter, N=newton, s=second

Second

The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....

, W=watt

Watt

The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...

, kg=kilogram

Kilogram

The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

, Ω=ohm

Ohm

The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...

For electronics, one farad is a fairly large amount of capacitance. The most commonly used submultiples

SI prefix

The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...

in electrical and electronic usage are the microfarad, nanofarad and picofarad.

## History

The farad was coined by Josiah Latimer Clark in the year of 1861, in honor of Michael FaradayMichael Faraday

Michael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....

, but it was for a unit of quantity of charge.

## Explanation

Values of capacitors are usually specified in ranges of**farads**(F),**microfarads**(μF),**nanofarads**(nF) or**picofarads**(pF).The size of commercially available capacitors ranges from around 100 fF (femtofarads, 10

^{-15}F) to 5 kF (kilofarads, 10^{3}F) ultracapacitors.When speaking of capacitor values a

*picofarad*is sometimes referred to as a*"puff"*or*"pic"*, as in "a ten puff capacitor". If the Greek letter μMu (letter)

Carlos Alberto Vives Restrepo is a Grammy Award and three-time Latin Grammy Award winning-Colombian singer, composer and actor.-Biography:...

is not available, the notation

*uF*is often used as a substitute for*μF*in electronics literature. A*micro-microfarad*(μμF), an obsolete unit sometimes found in older texts, is the equivalent of a*picofarad*. The*millifarad*is less used in practice, so that a capacitance of 4.7 F, for example, is sometimes written as 4,700 µF. North American usage also avoids*nanofarads*: a capacitance of 1 F will frequently be indicated as 1000 pF; and a capacitance of 1 F as 0.1 μF.The 'farad' should not be confused with the faraday, which is the electric charge carried by one mole

Mole (unit)

The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...

of singly charged ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s.

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

Daraf

The daraf is the unit of electrical elastance , the voltage across a capacitor after accepting an electric charge of 1 coulomb; it is the reciprocal of the farad...

.

A capacitor consists of two conducting surfaces, frequently referred to as plates, separated by an insulating layer usually referred to as a dielectric

Dielectric

A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...

. The original capacitor was the Leyden jar

Leyden jar

A Leyden jar, or Leiden jar, is a device that "stores" static electricity between two electrodes on the inside and outside of a jar. It was invented independently by German cleric Ewald Georg von Kleist on 11 October 1745 and by Dutch scientist Pieter van Musschenbroek of Leiden in 1745–1746. The...

developed in the 18th century. It is the accumulation

Accumulation

Accumulation may refer to:* Accumulation: None, a 2002 lo-fi album* Capital accumulation, the gathering of objects of value* Glacier ice accumulation, an element in the glacier mass balance formula...

of electric charge on the plates that results in capacitance

Capacitance

In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...

. Modern capacitors are constructed using a range of manufacturing techniques and materials to provide the extraordinarily wide range of capacitance values used in electronics

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

applications from femtofarads to farads, with

*voltage withstand capabilities*ranging from a few voltVolt

The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...

s to several kilovolts.

One picofarad is about the smallest value of capacitor available for general use in electronic design, since smaller capacitors would be dominated by the parasitic capacitances (stray capacitance) of other components, wiring or printed circuit board

Printed circuit board

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...

s. When capacitance values of 1 pF or lower are required, engineers sometimes create their own capacitors by twisting two short lengths of insulated wire together.

The capacitance of the Earth's ionosphere

Ionosphere

The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...

with respect to the ground is calculated to be about 1.8 F.

## Abfarads in medicine

An**abfarad**is an obsolete electromagnetic (CGS) unit of capacitance equal to 10^{9}farads (1,000,000,000 F or 1 GFGiga

Giga is a unit prefix in the metric system denoting a factor of billion . It has the symbol G.Giga is derived from the Greek γίγας, meaning 'giant'...

). This very large unit is used in medical terminology only.

The

**statfarad**was the comparable obsolete electrostatic (CGS) unit of capacitance, and was equal to 1 microfarad.