The coulomb (unit symbol: C) is the SI derived unit of electric charge (symbol: Q or q). 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:
Name and notation 
This SI unit is named after Charles-Augustin de Coulomb. As with every International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (C). However, when an SI unit is spelled out in English, it should always begin with a lower case 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 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.
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 
SI multiples for coulomb (C)
|Common multiples are in bold face.
See also SI prefix.
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 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 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 ≈ 1.4 A⋅h. After that charge has flowed, the battery must be discarded or recharged.
- According to Coulomb's Law, two negative 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.
See also 
- ^ a b c d Mohr, Peter J.; Taylor, Barry N.; Newell, David B. (2008). "CODATA Recommended Values of the Fundamental Physical Constants: 2006". Rev. Mod. Phys. 80 (2): 633–730. Bibcode:2008RvMP...80..633M. doi:10.1103/RevModPhys.80.633. Direct link to value. The inverse value (the number of elementary charges in 1C) is given by 1/[1.602176487(40)×10-19] = 6.24150965(16)×1018.
- ^ "SI Brochure, Appendix 1,". BIPM. p. 144.
- ^ "SI brochure, section 2.2.2". BIPM.
- ^ "SI brochure, section 126.96.36.199". BIPM.
- ^ "SI brochure, section 188.8.131.52". BIPM.
- ^ a b "Watt Balance". BIPM.
- ^ a b c d 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. Bibcode:2005Metro..42...71M. doi:10.1088/0026-1394/42/2/001.
- ^ Report of the CCU to the 23rd CGPM
- ^ Anon (November 2010). "BIPM Bulletin". BIPM. Retrieved 2011-01-28.
- ^ Martin Karl W. Pohl. "Physics: Principles with Applications". DESY.
- ^ Hasbrouck, Richard. Mitigating Lightning Hazards, Science & Technology Review May 1996. Retrieved on 2009-04-26.
- ^ How to do everything with digital photography – David Huss at Google Books, "The capacity range of an AA battery is typically from 1100–2200 mAh."