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Homework Help: Circuit with resistors. help me please!

  1. Feb 7, 2010 #1
    1. The problem statement, all variables and given/known data
    We are given currents ia and ib, 4A and 2A respectively. We must find ig and vg (tough). I understand how to do b and d easily once I get the unknowns (ig and vg), that's what I need help with.

    Picture >
    http://img210.imageshack.us/img210/3667/1000943d.jpg [Broken]

    3. The attempt at a solution
    I understand we need to find what the total resistance is, but I don't know how to simplify. My best bet is to use the formula to transform a resistors in shape of a T into a triangle. But would that work given a current inside the T? and not a resistor? Any ideas where to start?
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 7, 2010 #2
    If you transform the resistors you will lose the given information.To solve the problem,assign a current at every brunch and use KCL at every essential node.
  4. Feb 8, 2010 #3
    You can simplify the circuit somewhat by combining the series resistances, but that wont help much with the analysis.

    Zayer is right, you need to assign current variables through the remaining branches to generate some KCL equations. Below is a picture of the revised circuit.

    http://img202.imageshack.us/img202/7576/0208001255.jpg" [Broken]

    The variables vg, ig, ia, and ib with the addition of i1, i2, and i3 gives you seven unknown quantities. You can get four KCL equations from nodes A, B, C, and D shown in my circuit above. Add in three KVL equation around the loops ADCA, ACBA, and DBCD and you'll have seven circuit equations with seven unknowns. Then just sit back and let your linear algebra technique of choice do the rest.
    Last edited by a moderator: May 4, 2017
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