Coulomb

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For other uses, see Coulomb (disambiguation).
coulomb
Unit system: SI derived unit
Quantity: Electric charge
Symbol: C
Dimension: T⋅I
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[1]

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:

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}

Contents

Name and notation [edit]

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.[2]

Definition [edit]

In the SI system, the coulomb is defined in terms of the ampere and second: 1C = 1A × 1s.[3] The second is defined in terms of a frequency which is naturally emitted by caesium atoms.[4] The ampere is defined using Ampère's force law;[5] the definition relies in part on the mass of the international prototype kilogram, a metal cylinder housed in France.[6] In practice, the watt balance is used to measure amperes with the highest possible accuracy.[6]

SI prefixes [edit]

SI multiples for coulomb (C)
Submultiples Multiples
Value Symbol Name Value Symbol Name
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 zeptocoulomb 1021 C ZC zettacoulomb
10−24 C yC yoctocoulomb 1024 C YC yottacoulomb
Common multiples are in bold face.

See also SI prefix.

Conversions [edit]

Relation to elementary charge [edit]

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.[1] 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.[7] 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/(K_JR_K) is also an exact defined value in this unit system.[7] Specifically, e_{90} = (2 \times 10^{-9})/(25812.807 \times 483597.9) C exactly.[7] SI itself may someday change its definitions in a similar way.[7] 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"[8] This proposal is not yet accepted as part of the SI system: The SI definitions are unlikely to change until at least 2015.[9]

In everyday terms [edit]

  • The charges in static electricity from rubbing materials together are typically a few microcoulombs.[10]
  • The amount of charge that travels through a lightning bolt is typically around 15 C, although large bolts can be up to 350 C.[11]
  • 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.[12]
  • 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 [edit]

References [edit]

  1. ^ 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.
  2. ^ "SI Brochure, Appendix 1,". BIPM. p. 144. 
  3. ^ "SI brochure, section 2.2.2". BIPM. 
  4. ^ "SI brochure, section 2.2.1.3". BIPM. 
  5. ^ "SI brochure, section 2.2.1.4". BIPM. 
  6. ^ a b "Watt Balance". BIPM. 
  7. ^ 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.  edit
  8. ^ Report of the CCU to the 23rd CGPM
  9. ^ Anon (November 2010). "BIPM Bulletin". BIPM. Retrieved 2011-01-28. 
  10. ^ Martin Karl W. Pohl. "Physics: Principles with Applications". DESY. 
  11. ^ Hasbrouck, Richard. Mitigating Lightning Hazards, Science & Technology Review May 1996. Retrieved on 2009-04-26.
  12. ^ 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."
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Derived units
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