Coulomb

From Wikipedia, the free encyclopedia

Jump to: navigation, search
For other uses, see Coulomb (disambiguation).

The coulomb (symbol: C) is the SI derived unit of electric charge. It is named after Charles-Augustin de Coulomb.

Contents

[edit] Definition

One coulomb is the amount of electric charge transported in one second by a steady current of one ampere.[1][2][3]

1 \mathrm{C} = 1 \mathrm{A} \cdot 1 \mathrm{s}

One coulomb is the amount of charge stored by a capacitance of one farad charged to a potential difference of one volt:

1 \mathrm{C} = 1 \mathrm{F} \cdot 1 \mathrm{V}

[edit] Explanation

In principle, the coulomb could be defined in terms of the charge of an electron or elementary charge. Since the values of the Josephson (CIPM (1988) Recommendation 1, PV 56; 19) and von Klitzing (CIPM (1988), Recommendation 2, PV 56; 20) constants have been given conventional values (KJ ≡ 4.835 979 × 1014 Hz/V and RK ≡ 2.581 280 7 × 104 Ω), it is possible to combine these values to form an alternative (not yet official) definition of the coulomb. A coulomb is then equal to exactly 6.241 509 629 152 65 × 1018 elementary charges. Combined with the present definition of the ampere, this proposed definition would make the kilogram a derived unit.

Batteries are usually rated in milliampere-hours. A typical AA battery is rated at 2890 mA·h which converts to 10,404 C.[4]

In everyday situations, positive and negative charges are usually balanced out. According to Coulomb's Law, two point charges of +1 C, one meter apart, would experience a repulsive force of 9 × 109 N, roughly the equivalent of 900,000 metric tons of weight.

[edit] SI multiples

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.

[edit] Conversions

  • The magnitude of the electrical charge of one mole of electrons (approximately 6.022 × 1023 electrons, or Avogadro's number) is known as a faraday. One faraday equals 96485.3399 coulombs (the Faraday constant). In terms of Avogadro's number (NA), one coulomb is equal to approximately 1.036 × NA  × 10−5 elementary charges.
  • 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 amount of electrical charge in 6.241506 × 1018 electrons or other elementary charged particles.

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 uppercase (C). When an SI unit is spelled out in English, it should always begin with a lowercase 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.


[edit] See also

[edit] References

  1. ^ BIPM Table 3
  2. ^ NIST: Table 3. SI derived units with special names
  3. ^ BIPM SI Brochure, Appendix 1, p. 144
  4. ^ Alkaline Technical Information. Energizer. Retrieved 11 July 2007.
Retrieved from "http://en.wikipedia.org/wiki/Coulomb"
Personal tools