Coulombs

Coulombs‏‎

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: 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.

Definition  In the SI system, the coulomb is defined in terms of the ampere and second: 1 C = 1 A × 1 s.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.

Since the charge of one electron is known to be about 1.60217657×10^−19 coulombs, a coulomb can also be considered to be the charge of roughly 6.241509324×10^18 electrons (or protons; electrons are technically represented with a charge in negative coulombs, and protons positive, but protons do not move in a metal wire circuit, electrons do; for electrical purposes charge is generally represented with an absolute value), though this is not standard practice, and does not define the unit in any official sense.