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Thevenin Equal Resistance - Strange Circuit

  1. Feb 15, 2009 #1
    1. The problem statement, all variables and given/known data

    I want to find Rτ (Thevenin Equal Resistance) if the load is R4 in the attached image's circuit.
    As easy it may seem, I get confused because it asks for the equal resistance between A and B.

    2. Relevant equations



    3. The attempt at a solution

    We remove the voltage sources and s/c them. Then we have: R1 is parallel to (R2+R3) -> R1//(R2+R3).
    R5 parallel to the rest. So we have in total: Rτ= [R1//(R2+R3)] // R5
     

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    Last edited: Feb 15, 2009
  2. jcsd
  3. Feb 15, 2009 #2

    Redbelly98

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    Welcome to PF :smile:

    I see no current sources in the figure, those are voltage sources. So, what do we do with voltage sources?

    Also, note R2 & R3 are not actually in series. Because node A has a path leading to R4, they (R2 & R3) do not have an equal current going through them.
     
  4. Feb 15, 2009 #3
    Sorry my mistake. I meant Voltage sources. I need to find the Thevenin Equivalent Resistance if i take R4 as the load. So I replace voltage sources with short-circuit and also remove the load R4. From this point could you help me figure out the connections of the resistors ?

    Thanks again...
     
  5. Feb 15, 2009 #4
    Your approach looks ok. But the calculations are wrong. Check again how to calculate the paralleled resistances. Have you gotten ET already?
     
  6. Feb 15, 2009 #5
    I haven't done any calculations yet, I just indicated how I think the resistors are connected. No I just want to find RT
     
  7. Feb 15, 2009 #6
    Oh, okay. I thought those //'s were division marks.
     
  8. Feb 15, 2009 #7

    Redbelly98

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    I would redraw the figure (with voltage sources shorted), with "A" at the very top and "B" at the bottom. Redraw/move the resistors around until you see some that are in parallel or series, and combine them.
     
  9. Feb 15, 2009 #8
    I came up with this one, but the equivalent is different than the first one i posted ( Rτ= [R1//(R2+R3)] // R5 )

    In this case it is: RΤ=[(R1+R2)//R3 + R5]

    Please give me any hint as I am very confused.
    Thanks a lot
     

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  10. Feb 16, 2009 #9
    I'm not sure if this is any help to you, but what can be said about any open circuit (i.e. unconnected wires)?
     
    Last edited: Feb 16, 2009
  11. Feb 16, 2009 #10

    Redbelly98

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    There's some problems with your figure. Just for example, R2 should connect between A & B, after Vs2 is shorted.
     
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