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Homework Help: AC nodal anaylsis to find V thevenin

  1. Apr 25, 2015 #1
    1. The problem statement, all variables and given/known data
    Here is the circuit. I have to solve for V Thevenin

    I am having trouble figuring out what I am doing wrong here. I need to solve for Vth and I do, but it does not match with what my TA posted as the solution.


    2. Relevant equations
    The equations I set up are the same as the above. VL is the node voltage on the jΩ inductor and Vth is the voltage on the right.

    3. The attempt at a solution
    1. -1∠0° + (VL)/j + (Vth)/(-.5j) = 0

    2. Vth - VL = .25Ic

    3. Ic = Vth/(-.5j)

    Substitute 3 into equation 2.

    4. Vth - VL = .5iVth

    Now solve the system of equations for 1. and 5.
    1. -1∠0° + (VL)/j + (Vth)/(-.5j) = 0
    5. Vth(1-.5i) -Vth = 0

    Vth = -0.4-0.8i

    VL = -0.8-0.6i

    Am I doing this correctly? The solutions my TA posted does not get this answer for Vth. She got Vth = .4 -.8i.

    Attached Files:

    Last edited: Apr 25, 2015
  2. jcsd
  3. Apr 25, 2015 #2


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    Gold Member

    Your TA has forgotten the "-" in front of ".4".
  4. Apr 25, 2015 #3
    He used VL-Vth = .25Ic. That is wrong correct?
  5. Apr 25, 2015 #4


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    Staff: Mentor

    What happened to VL?
  6. Apr 25, 2015 #5
    Sorry, a typo, the second Vth should be VL
  7. Apr 25, 2015 #6


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    Gold Member

    According to arrow and signs, it's wrong.
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