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Homework Help: Resistors in a Circuit

  1. Oct 31, 2009 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    Resistors in Series = R1 + R2 + R3... = Req
    Resistors in Parallel = 1/R1 + 1/R2 + 1/R3 ... = 1/Req

    3. The attempt at a solution

    Studying for a test. This sample exam went pretty well. I am having trouble with 3 out of the 20. I can't figure this one out.

    The bottom branch can be combined to be Req = 30 + 30 = 60 Ohms

    From there, I can't seem to find a way to combine the rest. I have the answer (B) but I can't collapse the circuit.
  2. jcsd
  3. Oct 31, 2009 #2
    The top right resistor is shorted out, so it has no effect. Imagine that it's erased from the diagram.
    The center point and point b are the same point.
    You have 30 in parallel with 30 in parallel with (30+30).
    1/[(1/30) + (1/30) + (1/{30+30})] = 12 ohms.
    Last edited: Oct 31, 2009
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