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Resistor Circuit

  1. Sep 17, 2013 #1
    9JJ356s.png

    Is it possible to simplify this circuit using just parallel and series definitions ?

    * A circuit is parallel to another circuit or several circuits if and only if they share common terminals; i.e. if both the branches touch each other's endpoints

    * Resistors can be connected in series; that is, the current flows through them one after another

    These are the definitions of resistors in series or parallel and according to these definitions none of these are in series or parallel.

    Ct0GdEr.jpg

    This was my attempt at making the circuit a bit easier to simplify but still could not see how any would fit into the definitions.
     
  2. jcsd
  3. Sep 17, 2013 #2

    berkeman

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    Welcome to the PF.

    Your 2nd image is missing the 1 Ohm resistor on the right side...

    I'm not seeing a way to simplify it offhand, so I would just solve the problem using KCL equations written at the nodes. Can you give that a go to see what answer you get?
     
  4. Sep 17, 2013 #3

    phinds

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    look for delta-Y transforms, which is the only alternative to (and derived from) doing your own loop analysis
     
  5. Sep 17, 2013 #4
    There is, look at the node between 6 ohm resistors. :)
     
  6. Sep 17, 2013 #5

    phinds

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    Uh ... huh?
     
  7. Sep 17, 2013 #6
    The circuit is symmetrical...can you figure it out now?
     
  8. Sep 17, 2013 #7

    phinds

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    Yes, I saw the symmetry but that doesn't seem to eliminate the need to do a delta-Y transform, which is the crux of the OP's problem.
     
  9. Sep 17, 2013 #8

    lewando

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    If you split the "bottom" 3-ohm resistor into two series 1.5-ohms...
     
  10. Sep 17, 2013 #9

    berkeman

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    Interesting. Initially I'd dismissed cutting the circuit in half to use its symmetry, but maybe now I see what you mean. I didn't think cutting the bottom resistor in half bought anything, but I think I see what you're getting at.
     
  11. Sep 17, 2013 #10

    phinds

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    Then you have done nothing, as far as I can see, to avoid the need for a delta-Y transform. I don't see that it buys you anything. Am I missing something. Can you do this without the delta-Y transform (or the equivalent loop analysis) ?
     
  12. Sep 17, 2013 #11

    berkeman

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    Yeah, so there is one more trick to the method that they are proposing. I think we should leave it to the OP to figure out what that trick is. And I think they should also try the wye-delta transformation that you are proposing, to see if he gets the same answer with both techniques (he should).
     
  13. Sep 18, 2013 #12
    Alright so I split the 3 ohm resistor, and then could I add a wire to make the 1.5 ohms resitors parallel to the 3 ohm resistors and take it from there ? ImageUploadedByPhysics Forums1379520496.690797.jpg
     
  14. Sep 18, 2013 #13
    Yep!
     
  15. Sep 18, 2013 #14
    Awesomee thanks a lot guys!
     
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