# Coulomb

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Coulomb
 coulomb Unit system: SI derived unit Unit of... Electric charge Symbol: C Named after: Charles-Augustin de Coulomb Unit conversions 1 C in... is equal to... SI base units 1 A s CGS units 2997924580 statC Atomic units 6.24150965(16)×1018 e

The coulomb (symbol: C) is the SI derived unit of electric charge. It is defined as the charge transported by a steady current of one ampere in one second: $1 \mathrm{C} = 1 \mathrm{A} \times 1 \mathrm{s}$

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: $1 \mathrm{C} = 1 \mathrm{F} \times 1 \mathrm{V}$

## Name and notation

This SI unit is named after Charles-Augustin de Coulomb. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (C). When an SI unit is spelled out in English, it should always begin with a lower case letter (coulomb), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase. —Based on The International System of Units, section 5.2. 

## Definition

In the SI system, the coulomb is defined in terms of the ampere and second: 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.

## SI prefixes

Submultiples Multiples Value Symbol Name Value 10−1 C dC decicoulomb 101 C daC decacoulomb 10−2 C cC centicoulomb 102 C hC hectocoulomb 10−3 C mC millicoulomb 103 C kC kilocoulomb 10−6 C µC microcoulomb 106 C MC megacoulomb 10−9 C nC nanocoulomb 109 C GC gigacoulomb 10−12 C pC picocoulomb 1012 C TC teracoulomb 10−15 C fC femtocoulomb 1015 C PC petacoulomb 10−18 C aC attocoulomb 1018 C EC exacoulomb 10−21 C zC not used 1021 C ZC zettacoulomb 10−24 C yC not used 1024 C YC yottacoulomb Common multiples are in bold face.

## Conversions

• The magnitude of the electrical charge of one mole of elementary charges (approximately 6.022×1023, or Avogadro's number) 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 (NA), one coulomb is equal to approximately 1.036 × NA ×10−5 elementary charges.
• one ampere-hour = 3600 C, 1 mAh = 3.6 C
• The elementary charge is 1.602176487×10−19 C
• One statcoulomb (statC), the CGS electrostatic unit of charge (esu), is approximately 3.3356×10−10 C or about 1/3 nC.
• One coulomb is the magnitude (absolute value) of electrical charge in 6.24150965(16)×1018 protons or electrons. 

## Relation to elementary charge

The elementary charge, the charge of a proton (equivalently, the negative of the charge of an electron), is approximately 1.602176487(40)×10−19 C. 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 KJ and von Klitzing constant RK are exact defined values (written KJ-90 and RK-90), and it follows that the elementary charge e = 2 / (KJRK) is also an exact defined value in this unit system. Specifically, $e_{90} = (2 \times 10^{-9})/(25812.807 \times 483597.9) C$ 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 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 electricity from rubbing materials together are typically a few microcoulombs.
• The amount of charge that travels through a lightning bolt is typically around 15 C, although large bolts can be up to 350 C.
• The amount of charge that travels through a typical alkaline AA battery is about 5 kC = 5000 C = 1400 mAh. After that charge has flowed, the battery must be discarded or recharged.
• According to Coulomb's Law, two point charges of +1 C, placed one meter apart, would experience a repulsive force of 9×109 N, a force roughly equal to the weight of 920,000 metric tons of mass on the surface of the Earth.

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### Look at other dictionaries:

• COULOMB (C. A.) — Charles Augustin Coulomb est l’une des personnalités les plus marquantes de l’histoire des sciences et des techniques. Ses travaux ont contribué à une meilleure connaissance des phénomènes de l’électricité, du magnétisme et de la mécanique… …   Encyclopédie Universelle

• coulomb — [ kulɔ̃ ] n. m. • 1881; de Coulomb, n. pr. ♦ Phys. Unité de mesure de quantité d électricité et de charge électrique égale à la quantité d électricité transportée en une seconde par un courant de un ampère (symb. C). Coulomb par kilogramme :… …   Encyclopédie Universelle

• coulomb — COULÓMB, coulombi, s.m. Unitate de măsură pentru sarcina electrică, egală cu cantitatea de electricitate care traversează într o secundă secţiunea unui conductor străbătut de un curent electric constant de 1 amper. [pr.: culómb] – Din fr. coulomb …   Dicționar Român

• Coulomb —    , COULOMB S LAW    Charles Augustin de Coulomb (1736 1806), born into a French noble family, had available all the advantages for a good education. He attended the engineering school at Mezieres, the first school of its kind, where he showed a …   Dictionary of eponyms

• Coulomb — Cou lomb (k?? l?n ), n. [From Coulomb, a French physicist and electrican.] (Physics) The standard unit of quantity in electrical measurements. It is the quantity of electricity conveyed in one second by the current produced by an electro motive… …   The Collaborative International Dictionary of English

• coulomb — 1881, named for French chemist Charles Augustin de Coulomb (1736 1806), who devised a method of measuring electrical quantity. It is the quantity of electricity conveyed in 1 second by a current of 1 ampere. The name is a French form of Columbus …   Etymology dictionary

• coulomb — (De Ch. de Coulomb, 1736 1806, físico francés). m. Fís. culombio …   Diccionario de la lengua española

• coulomb — ► NOUN Physics ▪ the unit of electric charge in the SI system, equal to the quantity of electricity conveyed in one second by a current of one ampere. ORIGIN named after the French military engineer Charles Augustin de Coulomb (1736 1806) …   English terms dictionary

• coulomb — [ko͞o′läm΄, ko͞o′lōm΄] n. [after C. A. de Coulomb (1736 1806), Fr physicist] the basic unit of electric charge in the SI and MKS systems, equal to the charge of 6.281 × 1018 electrons; the charge carried by a current of one ampere in one second… …   English World dictionary

• Coulomb — (spr. Kulong), Charles Augustin de C., geb. 1736 in Angouleme; war Offizier des königlichen Geniecorps u. ging nach Martinique; nach seiner Rückkehr nach Europa um 1776 in Rochefort angestellt, wurde er, da er gegen das Project der Minister war,… …   Pierer's Universal-Lexikon

• Coulomb  — Coulomb (C. Sekunden Ampere, Amperesekunde), Einheit der Elektrizitätsmenge, die Elektrizitätsmenge, die bei 1 Ampere in 1 Sekunde durch den Querschnitt der Leitung fließt. S. Elektrische Maßeinheiten …   Meyers Großes Konversations-Lexikon