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SI derived unit of electric charge
The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI).[1][2] It is defined to be equal to the electric charge delivered by a 1 ampere current in 1 second, with the elementary charge e as a defining constant in the SI.[2][1]
The SI defines the coulomb as "the quantity of electricity carried in 1 second by a current of 1 ampere" by fixing the value of the elementary charge, e = 1.602176634×10−19 C.[3] Inverting the relationship, the coulomb can be expressed in terms of the elementary charge: 1 C = e 1.602 176 634 × 10 − 19 = 10 19 1.602 176 634 e . {\displaystyle 1~\mathrm {C} ={\frac {e}{1.602\,176\,634\times 10^{-19}}}={\frac {10^{19}}{1.602\,176\,634}}~e.} It is approximately 6241509074460762607.776 e and is thus not an integer multiple of the elementary charge.
The coulomb was previously defined in terms of the ampere based on the force between two wires, as 1 A × 1 s.[4] The 2019 redefinition of the ampere and other SI base units fixed the numerical value of the elementary charge when expressed in coulombs and therefore fixed the value of the coulomb when expressed as a multiple of the fundamental charge.
Like other SI units, the coulomb can be modified by adding a prefix that multiplies it by a power of 10.
SI multiples of coulomb (C) Submultiples Multiples Value SI symbol Name Value SI 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 10−27 C rC rontocoulomb 1027 C RC ronnacoulomb 10−30 C qC quectocoulomb 1030 C QC quettacoulomb Common multiples are in bold face.The coulomb is named after Charles-Augustin de Coulomb. As with every SI unit named after a person, its symbol starts with an upper case letter (C), but when written in full, it follows the rules for capitalisation of a common noun; i.e., coulomb becomes capitalised at the beginning of a sentence and in titles but is otherwise in lower case.[9]
By 1878, the British Association for the Advancement of Science had defined the volt, ohm, and farad, but not the coulomb.[10] In 1881, the International Electrical Congress, now the International Electrotechnical Commission (IEC), approved the volt as the unit for electromotive force, the ampere as the unit for electric current, and the coulomb as the unit of electric charge.[11] At that time, the volt was defined as the potential difference [i.e., what is nowadays called the "voltage (difference)"] across a conductor when a current of one ampere dissipates one watt of power. The coulomb (later "absolute coulomb" or "abcoulomb" for disambiguation) was part of the EMU system of units. The "international coulomb" based on laboratory specifications for its measurement was introduced by the IEC in 1908. The entire set of "reproducible units" was abandoned in 1948 and the "international coulomb" became the modern coulomb.[12]
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