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Homework Help: Electric Current - Finding # of Electrons

  1. Mar 2, 2009 #1
    1. The problem statement, all variables and given/known data

    a) The potential difference in a simple circuit is 13 V and the resistance is 3 . What current I flows in the circuit? Answer in units of A.

    (I got I = 4.333 which is correct)

    b) How many electrons pass a given point in the circuit in 7 min?

    2. Relevant equations

    n = I*t/q

    3. The attempt at a solution
    I'm having trouble with Part B of the question.

    I used n = I*t/q, so 4.333A*420sec/1.6e^-19 = 1.1374e^22

    Also, one ampere is 1 C per second, so 4.333*6.241e^18*420sec = 1.1357e^22

    But both answers are wrong.
  2. jcsd
  3. Mar 2, 2009 #2


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    Homework Helper

    The first method looks good to me. (I'm not familiar with the mole of electrons approach.)
    Could it be a significant digits problem? The given numbers suggest rounding to 1 or 2 digits. If you want 5 digits, better find a more accurate value for e.
  4. Mar 2, 2009 #3
    Sigfigs aren't checked. But generally, the more digits the better.

    Other than that, you don't see anything wrong with my answer?
  5. Mar 2, 2009 #4


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    Homework Helper

    I got the same answer.
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