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Current Ionic Solution, Charges

  1. Sep 2, 2012 #1
    1. The problem statement, all variables and given/known data

    Current passes through a solution of sodium chloride. In 1.00 second, 2.68*10^16 Na+ ions arrive at the negative electrode and 3.92*10^16 Cl- ions arrive at the positive electrode. What is the current passing between the electrodes? Final answer must be in milliamperes.

    2. Relevant equations

    I = Q / Δt

    3. The attempt at a solution

    2.68*10^16 Na+ (1.6*10^-19 C) = 4.288 ma
    3.68*10^16 Cl- (-1.6*10^-19C) = -6.272 ma

    4.288 ma + (-6.272 ma) = -1.984 ma

    Why is this incorrect?
     
  2. jcsd
  3. Sep 2, 2012 #2
    The ions aren't traveling in the same direction.
     
  4. Sep 3, 2012 #3

    Borek

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    Staff: Mentor

    As far as I can tell OP accounted for that.

    Buy a new calculator.
     
  5. Sep 9, 2012 #4
    dQ/dt = I
    opposite charges moving in opposite directions. Depending on the reference point both are either positive or negative.
    Unless I'm missing something...
     
  6. Sep 9, 2012 #5

    Borek

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    Staff: Mentor

    OP treats one current as positive, other as negative - that's equivalent.

    And there is a simple math mistake in the final summation.
     
  7. Sep 9, 2012 #6
    I don't see how that is equivalent since they are moving in opposite directions.
    Say you have two charges one at point A and one at point B with one being positive and one being negative.
    If they both move to opposite points then the magnitude dQ is 2. I don't see why this problem is different.
     
  8. Sep 10, 2012 #7

    Borek

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    Staff: Mentor

    Sigh, you are right. Call it a senior moment.
     
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