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Homework Help: Superposition Theorem

  1. Sep 7, 2010 #1
    1. The problem statement, all variables and given/known data

    Hi all

    I have been struggling to find the right ans for the I(R1) in this circuit.

    First i consider only the voltage source by opening the current source. As such i find that I'(R1) = (4-0.7)/1K = 3.3mA

    Secondly i consider the current source by shorting the voltage source. Thus i derive I''(R1) = 3mA

    Finally i get I(R1) = I'(R1) + I''(R1) = 3.3m + 3m = 6.3mA

    However the ans seems to indicate as only 3.3mA.

    Please help to see if my reasoning is correct.

    [PLAIN]http://img823.imageshack.us/img823/8508/circuit.png [Broken]
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 7, 2010 #2


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    You've neglected the 20-ohm resistor completely. Try recalculating everything taking it into account.
  4. Sep 7, 2010 #3
    When you shorted the voltage source, I think you assumed you could combine the two voltage sources together like you did in the first part of the calculation, but you cant. Try calculating the current through R1 just one source at a time - the current source, V1, then V2.
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