Coulomb
Definition

The SI defines the coulomb by taking the value of the elementary charge e to be 1.602 176 634 × 10 C, but was previously defined in terms of the force between two wires. The coulomb was originally defined, using the latter definition of the ampere, as 1 A × 1 s. 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.

One coulomb is approximately 6 241 509 074 460 762 607.776 e (and is thus not an integer multiple of the elementary charge), where the number is the reciprocal of 1.602 176 634 × 10 C. The coulomb is exactly 1 C = 1 1.602 176 634 × 10 − 19 e. {\displaystyle 1~\mathrm {C} ={\frac {1}{1.602\,176\,634\times 10^{-19}}}~e.}
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