<P> This SI unit is named after Charles - Augustin de Coulomb . As with every International System of Units (SI) unit named for 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 material using title case . Note that "degree Celsius" conforms to this rule because the "d" is lowercase.--Based on The International System of Units, section 5.2 . </P> <P> The SI system defines the coulomb in terms of the ampere and second: 1 C = 1 A × 1 s . The second is defined in terms of a frequency 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 . </P> <P> Since the charge of one electron is known to be about 6981160217662079999 ♠ 1.602 176 6208 (98) × 10 C, 1 C can also be considered the charge of roughly 6.241 509 × 10 ^ electrons or + 1 C the charge of that many positrons or protons, where the number is the reciprocal of 1.602 177 × 10 ^ . </P> <P> The proposed redefinition of the ampere and other SI base units would have the effect of fixing the numerical value of the elementary charge to an explicit constant expressed in coulombs, and therefore it would implicitly fix the value of the coulomb when expressed as a multiple of the fundamental charge (the numerical values of those quantities are the multiplicative inverses of each other). </P>

What is the charge in coulombs of an electron