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Finding Rth of a basic circuit

  1. Feb 2, 2015 #1
    1. The problem statement, all variables and given/known data
    Determine the Thevenin equivalent with respect to the terminals a,b.

    2. Relevant equations
    Rth=Voc/Isc

    3. The attempt at a solution
    Right now I'm just trying to calculate Rth by removing the sources from the circuit. When I calculated the Rth using the node voltage/mesh current method I calculated it to be 20 kΩ.

    So right now my idea is I have to short out the voltage source and open the current source.

    I think(?) this means the 2kΩ, 20kΩ, and 5kΩ(maybe not) would be cancelled out and the rest of the circuit would be intact.

    So I calculated Rth based on the rest...

    (40kΩ+10kΩ)||50kΩ=25kΩ

    Can someone explain what I did wrong?

    I also tried doing
    (10kΩ+50kΩ)||20kΩ+5kΩ which gave me an answer of 20kΩ but I do not think I can add the 5kΩ resistor to the 20kΩ resistor in that order.
     

    Attached Files:

  2. jcsd
  3. Feb 2, 2015 #2

    Simon Bridge

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    shorting the voltage source means the 2k and 20k resistors are in parallel.
     
  4. Feb 2, 2015 #3
    (40kΩ+10kΩ)||50kΩ=25kΩ

    (25kΩ+5kΩ)||20kΩ=12kΩ

    12kΩ||2kΩ=1.74kΩ

    Am I suppose to ignore some of the resistors due to shorting the current source? What does opening it do to the 10kΩ or the 40kΩ resistor?

    Am I suppose to open the voltage source and short the circuit source or vise versa?
     
  5. Feb 2, 2015 #4

    Simon Bridge

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  6. Feb 2, 2015 #5

    NascentOxygen

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    It's a dependent current source.
     
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