Charge of one electron is known to be as $1.6$ x $10^{-19}$ C or alternative 1 Coulomb contains charge of $6.24$ x $10^{18}$ electrons. I am just wondering if these numbers are arbitrarily chosen or were derived through some calculations?

  • $\begingroup$ @FredericThomas Thanks. This actually should be an answer because I now know where that number is coming from. $\endgroup$ – PagMax Dec 10 '18 at 18:17
  • $\begingroup$ Also I think you meant It was NOT Coulomb $\endgroup$ – PagMax Dec 10 '18 at 18:18
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    $\begingroup$ It was not Coulomb who found the charge of an electron, it was R. Milikan in 1909 who measured for the first time the charge of an electron in a oil drop experiment (see more on Wikipedia "oil drop experiment"). Sorry a typo slipped in, now it's correct. $\endgroup$ – Frederic Thomas Dec 10 '18 at 18:53

1 Coulomb is defined as 1 As, where the Ampere is defined as a current producing a given amount of force between two ideal conductors, and the second is defined in multiples of the period of a transition in Cs. Since both definitions of Ampere and second are somewhat arbitrary, them combining to the numbers you have given is just as arbitrary.

Starting next year we will have a new definition of the Ampere, which is actually based on how many electrons flow through a conductor per second, so then the Coulomb is more directly defined in terms of electrons, but the number itself is just as arbitrary.

  • $\begingroup$ And before the ampere existed, the unit of charge was derived from the two practical units chosen by the BA in 1864: the units that we now call volt and ohm. Their values were convenient for electrical engineers. 1 A = 1 V/Ω $\endgroup$ – jkien Dec 10 '18 at 20:01

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