# Coulomb

Physical unit
Unit name Coulomb
Unit symbol ${\ displaystyle \ mathrm {C}}$
Physical quantity (s) Electric charge
Formula symbol ${\ displaystyle Q}$, ${\ displaystyle q}$
dimension ${\ displaystyle {\ mathsf {I \; T}}}$
system International system of units
In SI units ${\ displaystyle \ mathrm {1 \; C = 1 \; As}}$
Named after Charles Augustin de Coulomb
Derived from Amps , second

The coulomb [ kuˈlõː ] ( unit symbol : C, formerly Cb) is the derived SI unit of the electrical charge ( symbol Q or q ). It is named after the French physicist Charles Augustin de Coulomb .

1 Coulomb is the electric charge is transported within one second by the cross-section of a conductor in which an electric current of the strength of an ampere flows:

${\ displaystyle 1 \, \ mathrm {C} = 1 \, \ mathrm {A} \ cdot 1 \, \ mathrm {s}}$

The coulomb is therefore also referred to as the ampere second (As). The ampere hour (Ah) that is customary to indicate the battery capacity is 3600 As = 3600 C.

## definition

The definition of the units coulomb and ampere is based on the elementary charge , which has been determined to be exact , see International System of Units . ${\ displaystyle e = 1 {,} 602 \, 176 \, 634 \ cdot 10 ^ {- 19} \, \ mathrm {C}}$

## Historical

The Coulomb has replaced the electrostatic CGS unit ESU or Franklin (Fr):

{\ displaystyle {\ begin {alignedat} {2} & 1 \, \ mathrm {C} \ && {\ mathrel {\ widehat {=}}} {\ frac {10 \ cdot c_ {0}} {1 \, \ mathrm {m / s}}} \, \ mathrm {Fr} \\\ Leftrightarrow \ & 1 \, \ mathrm {C} \ && {\ mathrel {\ widehat {\ approx}}} \ 2,997,924,580 \, \ mathrm {Fr} \\\ Leftrightarrow \ & 3 {,} 335641 \ cdot 10 ^ {- 10} \, \ mathrm {C} \ && {\ mathrel {\ widehat {\ approx}}} \ 1 \, \ mathrm {Fr } \ end {alignedat}}}

at the speed of light ${\ displaystyle c_ {0} = 299,792,458 \ \ mathrm {m / s}.}$

The two English electrical engineers Josiah Latimer Clark and Charles Tilston Bright proposed the farad as a unit for the electrical charge in 1861 in honor of the English physicist Michael Faraday . In 1881, however , the International Electricity Congress established the coulomb as the unit for electrical charge and the farad as the unit for electrical capacity .

The current definition of the coulomb by determining the elementary charge was adopted on November 16, 2018 at the 26th General Conference on Weights and Measures and came into force on May 20, 2019. Previously, the ampere was defined as the Lorentz force of an electric current, and the coulomb as one ampere second.