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Thevenen help

  1. Jun 29, 2010 #1
    [PLAIN]http://img695.imageshack.us/img695/2420/physicsm.jpg [Broken]

    i need to find thevenen equivalent circuit using R5 as load

    Ε1=20V, Ε2=10V, R1=6Ω, R2=12Ω, R3= 25Ω, R4=20Ω,
    R5=10Ω, R6=5Ω, Ι=0,2Α.

    Vth = -5V


    but how much is Rth?

    i can see that R4 is in series with (R2+R1)||R3 and R6

    is this correct?

    so the circuit will be

    [PLAIN]http://img37.imageshack.us/img37/9126/62188572.jpg [Broken]

    please tell me if im correct or not i need to know for the exams :(
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 29, 2010 #2

    vela

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    Your calculation for Rth is correct, but I got a different value for Vth.
     
  4. Jun 30, 2010 #3
    i replaced the current source with a voltage source

    we have no current on teh second loop

    so the voltage source has 5V

    hence


    -E2 + 5V = -5V will be the Vth

    am i doing anything wrong?

    oh but we have current going through the voltage source

    so i have to find the current in the first loop

    E1 - E3 - I*(R1+R2+R3) = 0

    I = 15/43 = 0.348837209 A

    so Vth = -5 + (0.348837209*R3) = -5 + 8.72093023 = 3.72093023 V

    is this correct?

    so in the shape the + will be on top and - on bottom
     
    Last edited: Jun 30, 2010
  5. Jun 30, 2010 #4

    vela

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    Yes, that matches what I calculated.
     
  6. Jun 30, 2010 #5
    thanks a lot for your help :))
     
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