The unit of electric charge is the coulomb, named after Charles Augustin de Coulomb. This makes sense because Coulomb's law talks about the force between two charges. Likewise, it also makes sense to name unit of electric current after André-Marie Ampère, who too was a contemporary of Coulomb. But I have seen that the SI unit of capacitance is the farad, named after Michael Faraday. Why was Michael Faraday's name given to the unit of capacitance instead of any other electromagnetic unit? Likewise, why is the unit of electrical resistance or magnetic reactance named after Ohm, given that Ohm's law talks about the relationship between current and resistance, and electrical resistance can exist irrespective of Ohm's law. Similarly, I do not understand why the SI unit of magnetic flux density is named after Tesla (see a related post here), since he most contributed to electrical engineering. Further examples include the volt, siemens, weber, and henry (for electromotive force, electric conductance, magnetic flux, and inductance, respectively). Why were their names prioritized over other famous scientists, like Pierre Curie or Hippolyte Fizeau or Emil Lenz?

More generally: How were the names of the SI units relevant to electromagnetism decided on, and why were certain scientists prioritized over others?

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    $\begingroup$ Well known to whom? Volta was a celebrity for his pile, and Weber's mentor on electrodynamics was Gauss himself, the inspirer of the CGS system of units. And why should being famous be a requirement for getting due credit? They all contributed to studying quantities whose units are named after them. $\endgroup$
    – Conifold
    Commented Nov 20, 2020 at 22:32
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    $\begingroup$ I don't know about the downvote. However, choosing electromagnetic unit names and getting them internationally approved at the IEC (International Electrical Congress) was messy and not easy. Coulomb as the unit of charge was a last minute choice; initially farad and weber had been proposed. Ampere as the unit of current was also a last minute choice, initially galvat and weber had been proposed. Weber had the disadvantage of still being alive in 1881, when the first unit names were approved. Backdoor diplomacy was required. See also hsm.stackexchange.com/a/11297/2667 $\endgroup$
    – jkien
    Commented Nov 21, 2020 at 20:10
  • $\begingroup$ I've significantly edited the question and reopened it. Please go here if you'd like to discuss whether this question should be on-topic. $\endgroup$
    – Danu
    Commented Nov 26, 2020 at 20:44
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    $\begingroup$ I'd suggest that one of the main criteria was likely not the comparative popularity of the scientist, but the subjective aesthetic qualities of their surname, such as the ability to reduce it to a symbol that did not clash with others, the syllable count and pronounceability of the name, and so on. $\endgroup$
    – Steve
    Commented Feb 4, 2021 at 11:23
  • $\begingroup$ With so many scientists to honor, one may wonder why, contrary to the CGS system, where the unit of magnetic field intensity is called the Oersted, SI uses the compound phrase "Ampere metre", instead of a single name. $\endgroup$
    – Alfred
    Commented Jan 10, 2022 at 9:38

1 Answer 1


Actually, the farad was the term used for a unit of charge by Latimer Clark and Charles Bright in 1861 in honour of Michael Faraday.

But by 1873, it had become the unit of capacitance and was adopted as such by The British Association for the Advancement of Science by the first report of their Committee for the Selection and Nomenclature of Dynamic and Electrical Units chaired by Sir W Thomson in their 43rd meeting.

More, it was then adopted as such by the International Congress of Electricians held in Paris in 1881 as reported by The Electrician of that year.

The Tesla as the unit of magnetic induction was adopted much later. It was adopted by the General Conference on Weights and Measures held in 1960 and was proposed by the electrical engineer, France Avcin.


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