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Charge vs Coulomb - A paradox?

  1. May 17, 2014 #1
    Hi I'm wondering: The symbol of charge is Q but the SI unit of charge is coulumb which is the Charge of approximately 6.241×1018 electrons. But charge is not itself defined, only in terms of Coulomb, and coulomb is defined in termes of Charge. Its SI definition of Coulomb is the charge transported by a constant current of one ampere in one second:

    1C=1A*1s = (q/s)*s=q= charge,

    Here is the question
    It seems to me that Coulumbs are defined in termes Amps which are defined in terms of charge but charge itself is not a unit of measurement, so how is it possible to define coulumbs and amps in terms of charge when charge is a property and not something we can measure? Charge is part of the equation for Amps A=q/s and Coulumbs=1A*1s = (q/s)*s=q= charge, How does it make sense?
  2. jcsd
  3. May 17, 2014 #2


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    Science Advisor

    The Ampere is not defined in terms of Coulombs, it is defined as , "the constant current that will produce an attractive force of 2 × 10–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum."
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