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Charge of an electron in Coulombs?

  1. Jun 10, 2012 #1
    Is it correct that the charge of an electron in Coulombs is

    - 1,602 176 565(35) • 10-19 C ?

    By inserting this in the formular for current I = Q / t, that would make the current a negative number. I dont reckon having read about negative currents though. So what's the explaination for how the negative sign dissappears and currents end up always being positive?
     
  2. jcsd
  3. Jun 10, 2012 #2

    Doc Al

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    Current is usually defined as flowing in the direction of positive charge carriers. (Historically, it wasn't anticipated that the charge carriers in a wire, for instance, were actually negatively charged.) So if electrons move to the right, the current is defined as moving to the left.
     
  4. Jun 10, 2012 #3
    but is it correct that the charge of an electron in Coulombs is - 1,602 176 565(35) • 10^-19 ?
     
  5. Jun 10, 2012 #4

    Doc Al

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    Sure.
     
  6. Jun 10, 2012 #5
    so lets say.. 18 C would be then be 18 / (- 1,602 176 565(35) • 10^(-19)) electrons? That's a negative number, how is it possible to have a negative number of electons?
     
  7. Jun 10, 2012 #6

    Doc Al

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    What's 18 C? Obviously not the charge on a bunch of electrons. Realize that if something ordinarily neutral is missing a number of electrons, that it will have a positive charge.

    What problem are you trying to solve?
     
  8. Jun 10, 2012 #7
    In the text book that I have, it comes with this example:

    A 5 amp current flows for an hour. The total charge that passes by in such case, is Q = I • t = 5 A • 3600 s = 18000 C or 18000 Coulombs. Now how many electrons is that?
     
  9. Jun 10, 2012 #8

    Doc Al

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    Just divide by the magnitude of the electron charge. Don't get hung up with signs.
     
  10. Jun 10, 2012 #9
    So coulomb is not the unit for charge, but the unit for the magnitude of charge?
     
  11. Jun 10, 2012 #10

    Doc Al

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    You can think of it that way. That's why the charge on the electron is a negative number of Coulombs.
     
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