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Resistive circuit problem

  1. Dec 21, 2011 #1
    1. The problem statement, all variables and given/known data
    I need help solving this problem. I don't understand what to do when theres 2 voltage sources.
    The problem asks you to find the power absorbed at each resistor

    http://www.facebook.com/photo.php?fbid=2950199437043&set=a.2950198837028.2154160.1323079519&type=3&theater

    2. Relevant equations
    The book says that the power absorb at the 6 ohm is 24 Watt, at 4 ohm is 100 Watt, and at the 8 ohm is 72 Watt


    3. The attempt at a solution
    I thought maybe you could subtract the two voltages since the polarities are different and then use the current divider formula saying the total resistance is parallel resistance of the 6 and 4 ohm and then add the 8 ohm.
     

    Attached Files:

  2. jcsd
  3. Dec 21, 2011 #2

    NascentOxygen

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    Staff: Mentor

    There is a voltage source of 12 v connected directly across the terminals of the 6 ohm resistor, so that tells you the voltage across that resistor. End of story.

    Similarly, for the 4 ohm.
     
    Last edited: Dec 21, 2011
  4. Dec 21, 2011 #3

    NascentOxygen

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    Staff: Mentor

    The voltage across the 8 ohm resistor requires a little more understanding, but not much more. One end of it is held at -12v, and the other end is at -20v. All a resistor is concerned with is the voltage difference across its terminals. So use maths to subtract one of those voltages from the other, and that tells you the voltage difference between those two points.
     
  5. Dec 21, 2011 #4
    You should also note that those resistors are connected in a delta arrangement, one that is somewhat common in resistor network problems.

    If need be, they can be coverted to a wye arrangement to further simplify the analysis.

    In the case I think because the analysis is so straightforward, no conversion is required.
     
  6. Dec 21, 2011 #5

    gneill

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    Staff: Mentor

    Careful, if you apply a transformation then the components will no longer be the same as the original circuit and you won't be able to find the power in those original components!
     
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