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Simplifying Complex Resistor Circuits

  1. Oct 29, 2012 #1
    Simplifying "Complex" Resistor Circuits

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

    Question 1:

    I have an E&M test coming up and I'm having trouble simplifying complex circuits. Our teacher told us something about "pinching" the wires which I didn't really understand. I found the following link "http://www.allaboutcircuits.com/vol_1/chpt_7/3.html". I got the right solution for the homework problem using it but is this method reliable? Does it always work? Are there any other suggestions for tackling this type of problems?

    Question 2

    The attached problem is from homework. The question is what would an ohmmeter read between a and b. I don't understand these questions much. I simplified it to what is shown in the second attached image without much trouble. Now my intuition tells me that I should add these three remaining resistors (in series) and that's the answer (40.3 Ω) but that's apparently wrong. My teacher says that I should add the 7 Ω and 23.3 Ω together (in series). Then take the resulting 30.3 Ω resistor and add it with the 10 Ω (in parallel) and that gives 7.5 Ω, which is the correct answer. Can someone explain this to me please?

    Please excuse the weird looking lines in the diagrams. I'm new to Visio. Thanks.

    2. Relevant equations
    3. The attempt at a solution

    Attached.
     

    Attached Files:

  2. jcsd
  3. Oct 29, 2012 #2

    phinds

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    Re: Simplifying "Complex" Resistor Circuits

    Relative to points a and b, what is the parallel/series configuration? Don't get hung up on the particular way you have DRAWN them ... that is irrelevant. Follow the wires.
     
  4. Oct 29, 2012 #3
    Re: Simplifying "Complex" Resistor Circuits

    Could you please elaborate? Thanks.
     
  5. Oct 29, 2012 #4

    phinds

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    Re: Simplifying "Complex" Resistor Circuits

    Not really. Redraw the circuit based on points a and b, not on some arbtrary configuration and maybe you'll see it.
     
  6. Oct 30, 2012 #5

    SammyS

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    Re: Simplifying "Complex" Resistor Circuits

    attachment.php?attachmentid=52461&d=1351562575.jpgattachment.php?attachmentid=52462&d=1351562575.jpg

    Connect a battery across a & b. Now, what is the series/parallel combination for the resistors?
     
  7. Oct 30, 2012 #6
    Re: Simplifying "Complex" Resistor Circuits

    Thank you guys. I think I understand it better now after doing many similar problems. I just "followed the wires" :)
     
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