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

[edit] Definition

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

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

[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 (K_J ≡ 4.835 979 × 10¹⁴ Hz/V and R_K ≡ 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, a force roughly equal to the weight of 900,000 metric tons of mass.

[edit] SI prefixes

See also SI prefix.

[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 the Faraday constant or a faraday. One faraday equals 96485.3399 coulombs . In terms of Avogadro's number (N_A), one coulomb is equal to approximately 1.036 × N_A  × 10⁻⁵ elementary charges.
• one ampere-hour = 3600 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 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

• Abcoulomb, a cgs unit of charge
• Ampère's circuital law
• Faraday (unit), an obsolete unit
• Quantity of electricity

[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.