1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Thevenin Equivalent of AC RLC Circuit w/ Dependent Voltage

  1. Jun 15, 2016 #1
    1. The problem statement, all variables and given/known data
    Find Vth and Zth.
    frequency = 2kHz

    2. Relevant equations
    w = 2 * (pi) * f
    ZL = j w L
    ZC = -j / (w * C)
    V = I*Z
    ZR = R

    3. The attempt at a solution
    At first I tried using nodal analysis which I receive the value V = 0 v. I believe this is because this circuit only has dependent voltage sources. Therefore, the Vth is just 0 v.

    10mH ---> j125.7
    1uF ---> -j79.6
    100 ohms ---> 100
    w = 2*(pi)*2000 = 12566.37

    Essentially, I am stuck. I have some theories as to what I can do though. I remember from DC circuit analysis that we can either add a 1v or a 1A (the number is arbitrary) source between terminals a and b, but I'm not sure what to do beyond that. Could I add a 1A (i.e. 1*cos(wt)) between the terminals, and then do nodal analysis? Then after that, would I take that voltage and divide it by the 1A (1cos(wt)) AC source to get the Zth? And as I mentioned above, wouldn't the thevenin equivalent of this circuit not even have a Vth since there's no independent sources?
  2. jcsd
  3. Jun 15, 2016 #2


    User Avatar

    Staff: Mentor

    A zero value for the Thevenin voltage is reasonable; zero is a perfectly good real number.

    For the impedance, your suggested approach has merit: add a generic 2 kHz current source ##I## at the load terminals. Use nodal analysis again leaving that current source as a variable and solve for ##v_{ab}##. Note that the desired impedance is ##v_{ab} / I##.
  4. Jun 15, 2016 #3
    I tried it out and it worked! Thanks for your help! All this circuit stuff is starting to really make sense now!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted