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Parallel and Series Resistor Simplification HELP

  1. Apr 13, 2009 #1

    nlm

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    Hi,

    I need to simplify this circuit of resistors.

    1. The problem statement, all variables and given/known data

    Image of problem:
    http://img24.imageshack.us/img24/9206/resistor1.jpg [Broken]

    The Resistor equivalent is 9 ohms, and the solution for R is actually 15 ohms. However, I'm not sure how to get this answer. I think I am getting stuck at the point in my solution on step 4/5 where I seem to have 3 resistors connected to 1 node, but the circuit looks confusing.

    I attempted to simplify the resistors in step 5 as resistors in parallel, but I don't think I am getting the right answer.

    2. Relevant equations
    parallel = 1/Rtotal = 1/R1 + 1/R2 + 1/R3
    Series = Rtotal = R1 + R2 + R3


    3. The attempt at a solution

    Image of my solution:
    http://img24.imageshack.us/img24/4978/resistor2.jpg [Broken]

    Any help would be appreciated.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 19, 2009 #2

    Redbelly98

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    Staff Emeritus
    Science Advisor
    Homework Helper

    Sorry about the delayed response! :redface:

    In step 4, there is an extra line that shouldn't be there. Erase the vertical line segment that is directly to the left of the Rp combination

     
    Last edited by a moderator: May 4, 2017
  4. May 1, 2009 #3
    Somewhere along the line (I prefer the beginning) you need to notice the 30ohm resistor is shorted and has nothing to do with your circuit. Visually, using your step 3, you can imagine the current exiting the 5Ohm taking the path of least resistance (the short circuit wire) and flowing through the 3 parallel resistors strands.

    This type of problem is readily verifiable with SPICE, Multisim, similar EDA tools - where you can examine the current through each resistor.
     
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