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Homework Help: Find the equivalent resistance for the circuit in the figure.

  1. Jul 17, 2011 #1
    1. The problem statement, all variables and given/known data
    Find the equivalent resistance for the circuit in the figure. (Use the following as necessary: Vemf, R.)

    2. Relevant equations

    3. The attempt at a solution

    This problem isn't that hard, but I'm having trouble trying to visualize how to combine the resistors. The 2 most left Resistors are in parallel, as are the 2 most right ones. Those 4 are all in series with the middle resistor. How can you split it? I can't visualize it. Can anyone give me a hint?

    Attached Files:

  2. jcsd
  3. Jul 17, 2011 #2


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    Staff: Mentor

    The two most left resistors are not in parallel. Neither are the two rightmost resistors. In order to be in parallel, each end of each resistor in a pair must be directly tied together, with no other components in between. In the diagram, the central resistor is between one end of the "paired" resistors.

    You can approach this problem either by employing a Δ - Y transformation (look up Delta-Y transformation), or by using one of several circuit analysis methods involving KCL or KVL equations to find the total current, I, drawn from the voltage source. The resistance of the circuit would then be Vemf/I.

    If you're clever you might be able to conclude something about the voltage potential across the central resistor (symmetry of the circuit helps), then draw a further conclusion about the current flowing through it and what it implies about its affect on the overall circuit. Certain obvious simplifications would then make your life much easier :smile:.

    Probably best to start with the basic circuit analysis methods and then see how the results jibe with an 'intuitive' approach.
  4. Jul 19, 2011 #3
    you can also use http://en.wikipedia.org/wiki/Wheatstone_bridge" [Broken] method ... its quite simpler than Δ - Y, KCL, KVL
    Last edited by a moderator: May 5, 2017
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