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Homework Help: Kirchoff's Rules Problem

  1. Mar 5, 2017 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    V = IR
    P = IV
    3. The attempt at a solution
    The attempt is much too long to type out, so here is a link to a picture of my work.

    I'm mostly concerned about part C, because I've seen some similar problems and my answer has been different by a magnitude of 10. Does this work look sound?
  2. jcsd
  3. Mar 5, 2017 #2
    Looks right to me.
  4. Mar 5, 2017 #3
    As far as I can tell, part C looks fine (assuming that parts b. and c. are right). I do have two tips to share that might make things easier. One, if you remember the other formulas for power, like P=I^2*R, then you can skip a step or two. The second has to do with finding the currents. You have two mesh-currents in this problem, right? One on the left, one on the right. You kind of turned those two variables into three variables before you'd solved any of them, which really kind of complicates things a lot. Just solve for mesh-current 1 and mesh-current 2, then after you've found both of them you can say that the current through the 7 ohm resistor is just mesh-current 1, and the current through the 4 ohm resistor is just mesh-current 1 minus mesh current 2. I think you'll find you can solve the whole thing in much less steps that way.
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