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Question : Thevenins Equivalent

  1. Sep 11, 2011 #1
    1. The problem statement, all variables and given/known data

    http://img716.imageshack.us/img716/8021/69925791.jpg [Broken]

    Find The Thevenins Equivalent of the circuit shown .
    at the terminal a and b i think

    2. Relevant equations
    Vth = Rth(Ith)
    V= IR

    3. The attempt at a solution
    For Vth
    i tried using Nodal Analysis Having 4 Node Voltages

    but i dont know if the 5 ohms resistor and 8 ohms resistor is having flow of current in there?

    For Rth

    the Current source is change into open ckt.
    then solve by having 40 and 20 in series then parallel in 10 ohms
    therefor [(40+20)x10]/70 + 45 + 5 + 8 = 78 ohms = Rth


    So im wondering how should i get the Vth now,,
    And is Vth = Va + 35V and Vth = Vb +15 V ? or I = (Va + 35 - Vth) / 5 ohms
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 11, 2011 #2

    lewando

    User Avatar
    Gold Member

    It might be easier to find the short circuit current, ISC, using mesh analysis: 3 currents (1 of them you already know-->2 equations). Then VTH = ISCRTH.

    Not sure what you are doing here. Like, where's the 10 ohms coming from? The 70? Somehow, your answer is correct.
     
  4. Sep 11, 2011 #3
    oh sorry that 10 should be 30 ,,

    thx for the answer,, i got my Isc = 1.84 and Vth = 143.52

    tried to use that mesh analysis

    i got equations

    60V - 90 Ia - 40V +30 Isc = 0
    35V - 15V - Isc (5 +30 +45 +8) + 30 Ia +90 =0
    then by elimination
    igot Isc , correct me if im wrong thanks
     
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