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Homework Help: Potential difference

  1. Jun 5, 2012 #1
    1. The problem statement, all variables and given/known data
    The Cells in a circuit has 2V and 4V emfs and 2Ω and 6Ω internal resistance respectively. Find the potential difference between AB

    2. Relevant equations
    Kirchoff's Laws

    3. The attempt at a solution
    The attempts are in image

    Attached Files:

  2. jcsd
  3. Jun 5, 2012 #2
    AB seems to be a shortcircuit. That is a potential difference of 0, so if you end up getting that, it's nothing to worry about. If you got something other than 0, that's when you should be worried. :wink:

    Basically, you can think of a shortcircuit as taking a branch with a single resistor R, and doing R → 0. From V = IR, you see that I = V/R, so if R → 0, the only way to stop I from going to infinity and being a defined finite value, is to have V = 0, that is, the potential difference across a shortcircuit vanishes.
  4. Jun 5, 2012 #3


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    If VAB ≠ 0, then it would be I-i that goes to infinity.
  5. Jun 6, 2012 #4
    The I in my explanation was the I of an arbitrary branch in which a shortcircuit is produced, I didn't use the same circuit as the one given. That's why I said V = IR, and not V = (I-i)R.

    The I of my example would be extrapolated to whatever it need be, per particular circuit.
  6. Jun 6, 2012 #5
    Ok thanks for help, i got it
  7. Jun 6, 2012 #6
    You're welcome. :biggrin:
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