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Why isn't CHARGE a fundamental quantity rather than CURRENT?

  1. Jul 14, 2010 #1
    Almost all physics or engineering textbooks have a table of the SI units
    that are based on six fundamental quantities. The one that is listed for
    the quanity "electric current" is always "ampere". However, usually a few
    pages past this fundamental table lies a definition of the ampere. 1 ampere
    = 1 coulomb/second. This makes it sound more like a derived unit than a
    fundamental unit. It seems more likely that the fundamental quantity
    "electric current" should be replaced by the quantity "charge" and that the
    fundamental unit should be the coulomb. While amperes can be broken down
    into coulombs and seconds, the coulomb cannot be broken down (except to a
    specific count of electrons or protons). Why does there seem to be some
    contradiction between the definition of a fundamental quantity (a quantity
    that can't be described in terms of another quantity) and the definition of
    electric current? Why isn't charge along with the coulomb included in the
    fundamental quantities table?
  2. jcsd
  3. Jul 14, 2010 #2
    It's true that 1 amp=1 Coulomb/second but of course 1 Coulomb=1 Amp second.I think the choice of what's considered to be more fundamental is guided largely by the experimental ease by which the unit can be established.The Ampere is defined with reference to the force between parallel current carrying wires which presents experimental difficulties to establish exactly but nevertheless is measurable to a high degree of accuracy.If we don't define the Coulomb with reference to the Ampere then how else should we define it?There must be ways but I'm assuming that the experiments needed to establish the unit are less accurate than the ones currently used.Anyway,like yourself I feel that the Coulomb is more fundamental than the Ampere.
  4. Jul 14, 2010 #3


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    I wouldn't read very much into the fact that Amperes are an SI base unit, rather than Coulombs.
    Heck, moles are an SI base unit, and it's not even a measure of anything.
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