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Homework Help: Circuit Analysis : Using Kirchoffs

  1. Aug 30, 2011 #1
    1. The problem statement, all variables and given/known data
    http://img202.imageshack.us/img202/939/95788682.jpg [Broken]



    Find Vo
    Vo = -50V (given answer by my prof)

    2. Relevant equations
    KVL
    (Series) V=V1+V2
    (Parallel) V=V1=V2
    KCL
    Current toward the node = Current Away from the node
    V=IR

    3. The attempt at a solution

    i tried to solve for the i in the left ckt
    i=(6v+0.004Vo)/2k <-- 6v is in series with 0.004Vo (i think)

    by KCL at the right
    25i - (Vo/40k) - (Vo/10k) = 0 <--- 40k and 10k is in parallel so Voltage would be equal
    the substitute terms

    25((6v+0.004Vo)/2k) - (Vo/40k) - (Vo/10k) = 0
    Vo = 1kV <--- actually is not right XD



    so there it is,, what did i miss?

    Edit : (50v change to 6v)
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Aug 30, 2011 #2

    gneill

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    Staff: Mentor

    Where does the 6V come from in your equations? The diagram shows a 50V source.

    Also, the potential across the 2k resistor appears to be 50V - 0.004Vo. "Walk" around the loop in the direction of the current and it goes: 50V - i*2k - 0.004Vo = 0.
     
  4. Aug 30, 2011 #3

    Aw.. my mistake,, 50v at the left should be 6v Sorry :tongue:

    Edit: So there it is i changed the circuit.
     
  5. Aug 30, 2011 #4
    by referring to what you said sir,

    i= (6v-0.004Vo)/ 2k

    BY KCL
    then 25(i)-Vo/40k - Vo/10k = 0
    then substitute
    25((6v-0.004Vo)/2l)) -Vo/40k -Vo/10k = 0
    Therefore

    Vo = 428.57V

    Hmm :confused: still not the right answer ?
     
  6. Aug 30, 2011 #5

    gneill

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    Staff: Mentor

    Or perhaps it's the right answer to the wrong problem :smile:

    Your calculations appear to be sound for the circuit shown. Can you verify that the circuit matches the problem given?
     
  7. Aug 30, 2011 #6
    i double check the given here in my copy.. the circuit is right.. but not so sure about my computation :tongue:

    so what do you think.. maybe the answer given by my prof is wrong? Vo = -50V :confused:
     
  8. Aug 30, 2011 #7

    gneill

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    Staff: Mentor

    As I said, your computation looks correct for the circuit given. It is possible that your Prof was incorrect (or was misinterpreted?).
     
  9. Aug 30, 2011 #8
    Ahm ok :approve: Thx for Helping me :smile:
     
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