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For other uses, see .
The coulomb (unit symbol: C) is the
(SI) unit of . It is the charge (symbol: Q or q) transported by a constant current of one
{\displaystyle 1~{\text{C}}=1~{\text{A}}\cdot 1~{\text{s}}}
Thus, it is also the amount of excess charge on a
charged to a potential difference of one :
{\displaystyle 1~{\text{C}}=1~{\text{F}}\cdot 1~{\text{V}}}
It is equivalent to the charge of approximately 6.242×1018 (1.036×10-5 ) , and -1 C is equivalent to the charge of approximately 6.242×1018 .
unit is named after . As with every International System of Units (SI) unit named for a person, the first letter of its
(C). However, when an SI unit is spelled out in English, it should always begin with a
letter (coulomb)—except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using . Note that "degree " conforms to this rule because the "d" is lowercase.— Based on , section 5.2.
defines the coulomb in terms of the
and : 1 C = 1 A × 1 s. The second is defined in terms of a frequency naturally emitted by
atoms. The ampe the definition relies in part on the mass of the , a metal cylinder housed in France. In practice, the
is used to measure amperes with the highest possible accuracy.
Since the charge of one electron is known to be about -1.6021766208(98)×10-19 C, -1 C can also be considered the charge of roughly 6.241509×1018 electrons (or +1 C the charge of that many positrons or protons), where the number is the reciprocal of 1.602177×10-19.
and other SI base units would have the effect of fixing the numerical value of the fundamental charge to an explicit constant expressed in coulombs, and therefore it would implicitly fix the value of the coulomb when expressed as a multiple of the fundamental charge (the numerical values of those quantities are the
of each other).
SI multiples for coulomb (C)
Submultiples
decicoulomb
decacoulomb
centicoulomb
hectocoulomb
millicoulomb
kilocoulomb
microcoulomb
megacoulomb
nanocoulomb
gigacoulomb
picocoulomb
teracoulomb
femtocoulomb
petacoulomb
attocoulomb
exacoulomb
zeptocoulomb
zettacoulomb
yoctocoulomb
yottacoulomb
Common multiples are in bold face.
See also .
One coulomb is the magnitude () of electrical charge in 6.24150934(14)×1018
The inverse of this number gives the
of 1.6021766208(98)×10-19 C.
The magnitude of the electrical charge of one
(approximately 6.022×1023, or ) is known as a
(closely related to the ). One faraday equals 96485.3399 coulombs. In terms of Avogadro's number (NA), one coulomb is equal to approximately 1.036 × NA×10-5 elementary charges.
= ;C, 1 mA?h = 3.6 C.
(statC), the obsolete
electrostatic unit of charge (esu), is approximately 3.3356×10-10 C or about one-third of a nanocoulomb.
The , the charge of a proton (equivalently, the negative of the charge of an electron), is approximately 1.6021766208(98)×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 , the values of the
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, e90 = (2×10-9)/(25812.807 × 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 coulombs", (in which the numeric value is the 2006 CODATA recommended value, since superseded). This proposal is not yet accepted as part of the SI; the SI definitions are unlikely to change until at least 2015.
The charges in
from rubbing materials together are typically a few microcoulombs.
The amount of charge that travels through a
is typically around 15 C, although large bolts can be up to 350 C.
The amount of charge that travels through a typical
from being fully charged to discharged is about 5 kC = ;C ≈ ;.
According to , two negative
of -1 C, placed one meter apart, would experience a repulsive
of 9×109 N, a force roughly equal to the weight of 920000 metric tons of
on the surface of the Earth.
uses everyday terms to illustrate movement of charge and the transfer of energy. The analogy equates charge to a volume of water, and voltage to pressure. One coulomb equals (the negative of) the charge of 6.24×1018 electrons. The amount of energy transferred by the flow of 1 for example, 300 times fewer electrons flow through a lightning bolt than in the discharge of an AA battery, but the total energy transferred by the flow of the lightning's electrons is 300 million times greater.
, a cgs unit of charge
, an obsolete unit
6.24150934(14)×1018 is the reciprocal of the 2010 CODATA recommended value 1.602176565(35)×10-19 for the elementary charge in coulomb.
(PDF). BIPM. p. 144.
. The NIST Reference on Constants, Units, and Uncertainty. US . June 2015.
Mills, I. M.; Mohr, P. J.; Quinn, T. J.; Taylor, B. N.; Williams, E. R. (2005). "Redefinition of the kilogram: a decision whose time has come". Metrologia 42 (2): 71. :. :.
Anon (November 2010).
(PDF). BIPM.
Martin Karl W. Pohl.
Hasbrouck, Richard. , Science & Technology Review May 1996. Retrieved on .
, p. 23, at , "The capacity range of an AA battery is typically from