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Homework Help: Simple circuit.

  1. Dec 18, 2011 #1
    1. The problem statement, all variables and given/known data
    practiceprob.jpg


    2. Relevant equations
    I am trying to do some self study here before I take my circuits course. I am stuck on this problem for some reason.. The equation I am coming up with for the node is : 6 - Vo/2 - Io/4 - Vo/8 = 0.. After getting at equation I cant seem to come to the answer. Do I need to do another equation here? Thanks


    3. The attempt at a solution
     
  2. jcsd
  3. Dec 18, 2011 #2

    cepheid

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    Welcome to PF Would!

    Ohm's law for the 2 ohm resistor tells you that i0 = v0/(2 Ω). That's your second equation. Now you have everything in terms of only one unknown, and you can therefore solve the system.
     
  4. Dec 19, 2011 #3
    Thanks a lot for the help! I must be doing some simple math wrong here.. but im getting : 6 - Vo/2 - Vo/4 - Vo/8 = 0 then multiplying all of that by 8 to get 48- 4Vo - 2Vo - Vo = 0 then ultimately getting Vo = 6.85V but that is wrong... What am I doing wrong there? Should I be assuming that the current in across the 8 ohm resistor is moving upward and therefore making the equation 48 - 4Vo - 2Vo + Vo = 0? It works out that way but if it is like that could you tell me why? Since it is not marked i assumed it was a voltage drop across the 8 ohm resistor..
     
  5. Dec 19, 2011 #4

    cepheid

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    The third term in your equation is simply wrong. In your original KCL equation, this term was i0/4, which was correct. Then we determined that i0 = v0/2. Hence, i0/4 = (v0/2)/4 = v0/8. The third term (in red) should therefore be v0/8.
     
  6. Dec 19, 2011 #5
    Wow I feel stupid after looking back at that. Thank you for the help.
     
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