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Homework Help: Circuits Superposition Problem

  1. Jun 25, 2013 #1
    1. The problem statement, all variables and given/known data

    I have attached a pdf of the problem I am working on. The top circuit is the original problem; I am supposed to solve for the voltage drop across the 4-ohm resistor (top right). I HAVE to use the superposition theorem to solve this problem. The 4 circuits drawn below the top circuit are where I eliminated the current source in an attempt to solve for the currents/voltages on each resistor. Can someone please check my work thus far and let me know where I made a mistake? I think there is a mistake because when I take I*R fr each resistor and add them up, I get 28V which doesn't equal my 20V source. Thanks in advance for your help!

    2. Relevant equations

    3. The attempt at a solution

    See attached pdf.

    Attached Files:

  2. jcsd
  3. Jun 25, 2013 #2


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    Staff: Mentor

    Your result for the potential drop across the 4Ω resistor due to the 20V source looks fine. The currents that you've labeled also look okay. So my question would be, what sum of potential drops across resistors did you make that added to 28V? Note that all the resistors are not in series...
  4. Jul 1, 2013 #3

    rude man

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    Homework Helper
    Gold Member

    So far, so good - but keep in mind thast the current from your 4th figure is split between the 6 and the 12 ohm resistors and you really want the current thru the 12 ohm which is the current thru the 4 ohm which is what you're really after.

    So now do the current source!
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