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Deterimning Thevenin's circuit

  1. Apr 30, 2014 #1
    I have to determine the Thevenin's equivalent circuit for the circuit attached.
    I am stuck on the first and essential part, finding the thevenin's resistance.

    Answer should be 10ohms, my attempt:

    [itex]R_2||4 = \frac{5*16}{5+16} = 3.81ohms[/itex]

    [itex]R_1,3,5 = 20 + 12 + 2 = 34ohms[/itex]
     
  2. jcsd
  3. Apr 30, 2014 #2
    Ok, so R2 AND R4 are not in parallel. Are R2 and R1 in parallel?
     
  4. Apr 30, 2014 #3

    phinds

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    Be a lot easier to figure out what you are talking about if you actually showed the circuit.
     
  5. Apr 30, 2014 #4

    gneill

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    Staff: Mentor

    [You forgot to attach your image. I've "borrowed" it from your previous thread]

    attachment.php?attachmentid=69249&stc=1&d=1398860411.gif

    Yes, when the source voltage E is suppressed then R1 and R2 will be in parallel.
     

    Attached Files:

  6. Apr 30, 2014 #5
    Sorry, i did but it wouldn't allow me since i already posted it in another post.

    So:

    [itex]R1||2=\frac{20*5}{20+5}=4ohms[/itex]
     
  7. Apr 30, 2014 #6
    Are R3 an R4 parallel?
     
  8. Apr 30, 2014 #7

    gneill

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    No. Once you've combined R1 and R2, redraw your circuit including the "new" resistance (maybe call it R12) and re-evaluate the layout.
     
  9. Apr 30, 2014 #8
    Is that new resistance positioned where R2 is or where R1 is?
     
  10. Apr 30, 2014 #9

    gneill

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    Either. It's replacing both, which were in parallel, so they make the same node connections in the circuit. Note that the orientation (vertical, horizontal, diagonal,...) on a drawing makes no difference to the electrical behavior of the circuit. The only thing that matters is the connections.
     
  11. Apr 30, 2014 #10
    so...
     

    Attached Files:

    • c2.jpg
      c2.jpg
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  12. Apr 30, 2014 #11

    gneill

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    Staff: Mentor

    Sure. Keep on going...

    I assume that you're using the voltage source in your image as a placeholder for the eventual Thevenin voltage source. If you're clever you can give it a value as you work your way through the circuit reductions; you can successively replace the portions of the circuit you reduce with Thevenin equivalents (Voltage and resistance) and eventually end up with the final overall Thevenin equivalent.

    attachment.php?attachmentid=69251&stc=1&d=1398862991.gif
     

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