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Homework Help: Calculate the total resistance of the circuit

  1. Jun 25, 2013 #1
    1. The problem statement, all variables and given/known data
    Here is the circuit -

    Calculate the total resistance between A and B. ( All resistance are in ohms)

    2. Relevant equations


    3. The attempt at a solution

    The wire which runs across the diagonal from upper left to lower right WITHOUT crossing the other diagonal wire is the thing of problem for me. I can't detect any resistors in parallel or series ! What should I do? Please help !
  2. jcsd
  3. Jun 25, 2013 #2


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    Staff: Mentor

    You can move the components around in the drawing so long as you don't change any of the connections (what's connected to what). Wires can be considered flexible, extendible, and contractible. Any contiguous wire path is the same node, and you can move the connections to that node around as much as you like. So...

    That diagonal wire connects the bottom right corner to the top left, which makes it the same node. Call it node A, since terminal A connects there. Suppose you now think about what would happen if that diagonal wire were to contract, pulling the bottom right corner up to the top left corner. How does the circuit look now?
  4. Jun 25, 2013 #3
    Now that is a good hint !
    Let me redraw -
    But now the two 10 ohm resistors are in series or parallel?
  5. Jun 25, 2013 #4


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    Staff: Mentor

    Are both ends of each pair tied together, or only one end of each resistor?


    Attached Files:

  6. Jun 25, 2013 #5
    Great so they are in parallel so both evaluate to 5.
    Then the top one is in series with the 10 ohm one. So 5+10 =15 ohm which is in parallel with 5 ohm so answer = 5*15/20=75/20=15/4 which is the correct answer!
    Thanks a lot ! PF is awesome.
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