Coulomb

Overview

**coulomb**is the SI

Si

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

derived unit of electric charge

Electric 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...

. It is defined as the charge transported by a steady current of one 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...

in one 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....

:

One coulomb is also the amount of excess charge on the positive side of a 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...

of one farad

Farad

The farad is the SI unit of capacitance. The unit is named after the English physicist Michael Faraday.- Definition :A farad is the charge in coulombs which a capacitor will accept for the potential across it to change 1 volt. A coulomb is 1 ampere second...

charged to a potential difference of one 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...

:

In the SI system, the coulomb is defined in terms of the 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...

and 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....

: 1C = 1A × 1s.

Discussions

Encyclopedia

The

derived unit of electric charge

. It is defined as the charge transported by a steady current of one ampere

in one second

:

One coulomb is also the amount of excess charge on the positive side of a capacitance

of one farad

charged to a potential difference of one volt

:

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...

and secondThe 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....

: 1C = 1A × 1s. The second is defined in terms of a frequency which is naturally emitted by caesium

atoms. The ampere is defined using Ampère's force law

; the definition relies in part on the mass of the international prototype kilogram

, a metal cylinder housed in France. In practice, the watt balance

is used to measure amperes with the highest possible accuracy.

, the charge of a proton (equivalently, the negative of the charge of an electron), is approximately . In SI, the elementary charge in coulombs is an approximate value: no experiment can be infinitely accurate. However, in other unit systems, the elementary charge has an

**coulomb**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...

derived unit of electric charge

Electric 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...

. It is defined as the charge transported by a steady current of one 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...

in one 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....

:

One coulomb is also the amount of excess charge on the positive side of a 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...

of one farad

Farad

The farad is the SI unit of capacitance. The unit is named after the English physicist Michael Faraday.- Definition :A farad is the charge in coulombs which a capacitor will accept for the potential across it to change 1 volt. A coulomb is 1 ampere second...

charged to a potential difference of one 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...

:

## Definition

In the SI system, the coulomb is defined in terms of the ampereAmpere

and second

Second

: 1C = 1A × 1s. The second is defined in terms of a frequency which is naturally emitted by caesium

Caesium

Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

atoms. The ampere is defined using Ampère's force law

Ampère's force law

In magnetostatics, the force of attraction or repulsion between two current-carrying wires is often called Ampère's force law...

; the definition relies in part on the mass of the international prototype 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...

, a metal cylinder housed in France. In practice, the watt balance

Watt balance

The watt balance is an experimental electromechanical weight measuring instrument that measures the weight of a test object very precisely by the strength of an electric current and a voltage. It is being developed as a metrological instrument that may one day provide a definition of the kilogram...

is used to measure amperes with the highest possible accuracy.

## SI prefixes

See also SI prefix.## Conversions

- The magnitude of the electrical charge of one moleMole (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 elementary chargeElementary chargeThe elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...

s (approximately 6.022, or Avogadro's numberAvogadro's numberIn chemistry and physics, the Avogadro constant is defined as the ratio of the number of constituent particles N in a sample to the amount of substance n through the relationship NA = N/n. Thus, it is the proportionality factor that relates the molar mass of an entity, i.e...

) is known as a faraday unit of charge (closely related to the Faraday constant). One faraday is equal to 96485.3399 coulombs. In terms of Avogadro's number (*N*_{A}), one coulomb is equal to approximately 1.036 ×*N*_{A}elementary charges. - one ampere-hourAmpere-hourAn ampere-hour or amp-hour is a unit of electric charge, with sub-units milliampere-hour and milliampere second...

= 3600 C, 1 mAh = 3.6 C - The elementary chargeElementary chargeThe elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...

is 1.602176487 C - One statcoulombStatcoulombThe statcoulomb or franklin or electrostatic unit of charge is the physical unit for electrical charge used in the centimetre-gram-second system of units and Gaussian units. It is a derived unit given by...

(statC), the CGS electrostatic unit of charge (esu), is approximately 3.3356 C or about 1/3 nC. - One coulomb is the magnitude (absolute valueAbsolute valueIn mathematics, the absolute value |a| of a real number a is the numerical value of a without regard to its sign. So, for example, the absolute value of 3 is 3, and the absolute value of -3 is also 3...

) of electrical charge in protonProtonThe proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s or electronElectronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s.

## Relation to elementary charge

The elementary chargeElementary charge

The elementary charge, usually denoted as e, is the electric charge carried by a single proton, or equivalently, the absolute value of the electric charge carried by a single electron. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called...

, the charge of a proton (equivalently, the negative of the charge of an electron), is approximately . In SI, the elementary charge in coulombs is an approximate value: no experiment can be infinitely accurate. However, in other unit systems, the elementary charge has an

*exact*value by definition, and other charges are ultimately measured relative to the elementary charge. For example, in conventional electrical units, the values of the Josephson constant*K*and von Klitzing constant_{J}*R*are exact defined values (written_{K}*K*and_{J-90}*R*), and it follows that the elementary charge is also an exact defined value in this unit system. Specifically, exactly. SI itself may someday change its definitions in a similar way. For example, one possible proposed redefinition is "the ampere...is [defined] such that the value of the elementary charge_{K-90}*e*(charge on a proton) is exactly 1.602176487×10^{−19}coulomb" This proposal is not yet accepted as part of the SI system: The SI definitions are unlikely to change until at least 2015.## In everyday terms

- The charges in static electricityStatic electricityStatic electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...

from rubbing materials together are typically a few microcoulombs. - The amount of charge that travels through a lightning boltLightningLightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

is typically around 15 C, although large bolts can be up to 350 C. - The amount of charge that travels through a typical alkalineAlkaline batteryAlkaline batteries are a type of primary batteries dependent upon the reaction between zinc and manganese dioxide . A rechargeable alkaline battery allows reuse of specially designed cells....

AA batteryAA batteryAn AA battery is a standard size of battery. Batteries of this size are the most commonly used type of in portable electronic devices. An AA battery is composed of a single electrochemical cell...

is about 5 kC = 5000 C = 1400 mAhMAHThe National Security Service was the governmental intelligence organization of Turkey between 1926 and 1965, when it was replaced by the National Intelligence Organization ....

. After that charge has flowed, the battery must be discarded or recharged. - According to Coulomb's LawCoulomb's lawCoulomb's law or Coulomb's inverse-square law, is a law of physics describing the electrostatic interaction between electrically charged particles. It was first published in 1785 by French physicist Charles Augustin de Coulomb and was essential to the development of the theory of electromagnetism...

, two point charges of +1 C, placed one meter apart, would experience a repulsive forceForceIn physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

of 9 N, a force roughly equal to the weight of 920,000 metric tons of massMassMass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

on the surface of the Earth.

## See also

- AbcoulombAbcoulombThe abcoulomb or electromagnetic unit of charge is the basic physical unit of electric charge in the cgs-emu system of units...

, a cgs unit of charge - Ampère's circuital law
- Coulomb's lawCoulomb's lawCoulomb's law or Coulomb's inverse-square law, is a law of physics describing the electrostatic interaction between electrically charged particles. It was first published in 1785 by French physicist Charles Augustin de Coulomb and was essential to the development of the theory of electromagnetism...
- ElectrostaticsElectrostaticsElectrostatics is the branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges....
- Elementary chargeElementary charge
- Faraday (unit), an obsolete unit
- Quantity of electricityQuantity of electricityIn physics the term quantity of electricity refers to the quantity of electric charge. It is designated by the letter Q and in the SI system is measured in derived units called Coulombs.- Pre-English origins :...