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Rth for a circuit

  1. Dec 16, 2014 #1
    1. The problem statement, all variables and given/known data
    Hi,

    I am trying to find Rth for this circuit but Im not sure if I've got it right, could someone give a hand?

    2. Relevant equations


    3. The attempt at a solution
    I think R3 can be omitted and R1, 2, and 4 are in series so the answer is 10k Ohms as R5 is in parallel to what was the power source (now a wire) can be omitted as well?

    Thanks!
     

    Attached Files:

  2. jcsd
  3. Dec 16, 2014 #2

    gneill

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    Staff: Mentor

    R3 cannot be omitted as there is no path from A to B that can avoid it.

    What's the procedure for finding the Thevenin resistance of a circuit?
     
  4. Dec 16, 2014 #3
    Really? I thought that when Vt has been replaced by a wire (as you do to fine Rth) then all the current can go through the new wire instead?
     
  5. Dec 16, 2014 #4

    gneill

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    Staff: Mentor

    Inject a current at A and show how it can get to B without passing through R3. Shorting the voltage supply (replacing with a wire) does not make a difference there. It does, however, let you eliminate another resistance...
     
  6. Dec 16, 2014 #5
    Oh sorry, I'm getting confused with R5. (You can get rid of R5 can't you?)
     
  7. Dec 16, 2014 #6

    gneill

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    Staff: Mentor

    Yup. Suppressing the voltage source shorts out R5, so their combined resistance is 0 Ohms.
     
  8. Dec 16, 2014 #7
    So then R1 and R4 are in series and that pair is in parallel to R2. That whole combination is then in series with R3 to make Rth 5.4 k Ohms? :)
     
  9. Dec 16, 2014 #8

    gneill

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    Staff: Mentor

    Yes! :approve:
     
  10. Dec 16, 2014 #9
    Yay! Thanks very much! :D
     
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