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Solving for Vo in terms of Vs/Vx

  1. May 22, 2013 #1
    http://imgur.com/xe52P30



    2. Vx= Vs(R1/R1+R2), V=IR



    3. I combined the 1k Ω and 5k Ω resistors then used voltage division to find Vx. I used Vx to find Vo which I found to be (5/18)Vx. I dont know where I can do KCL or KVL to solve for Vx.
     
    Last edited: May 22, 2013
  2. jcsd
  3. May 22, 2013 #2

    gneill

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    Staff: Mentor

    You used voltage division to find Vx. What did you get?

    Can you show your work for finding Vo in terms of Vx? The expression you gave doesn't look right to me.
     

    Attached Files:

  4. May 22, 2013 #3
    Doing voltage division I found Vx = (2/5)Vs. After combining the two resistors on the right side and doing ohm's law I found that Vo = (5/6)(1/.3)Vx = (mistake) is 5/1.8=2.8Vx.
     
  5. May 22, 2013 #4

    gneill

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    Check your value for the combined resistors. Pay attention to the units used. Also take a look at your current expression; why do you divide by 0.3S? The current is specified to be 0.3S*Vx.
     
  6. May 22, 2013 #5
    Does .3S not mean .3 Siemens = 1/Resistance ?
     
  7. May 22, 2013 #6

    gneill

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    Yes. And Volts x Siemens = Current. That's a controlled current source.
     
  8. May 22, 2013 #7
    Ok, so then Vo=.25Vx?, I also have Vx=.4Vs
     
  9. May 22, 2013 #8

    gneill

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    Again, what are the units for the two resistors in parallel? How many ohms does their parallel combination make? Your expression for Vx looks okay.
     
  10. May 22, 2013 #9
    They are in kiloohms, their parallel combination makes (5*1)/(5+1) = 5/6 kΩ, 833Ω
     
  11. May 22, 2013 #10

    gneill

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    Right. Or, if you want to retain accuracy, call it 5000/6 = 2500/3 Ohms. So multiplying your 0.3Vx by 2500/3 gives...
     
  12. May 22, 2013 #11
    Vo=250Ω*Vx, so now I have Vx = .4Vs and Vo = 250Vx. I could substituite Vx into Vo, but I do not have a value for Vs.
     
  13. May 22, 2013 #12

    gneill

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    Nor do you need one... you are looking for Vo in terms of Vs, so a symbolic solution is fine.
     
  14. May 22, 2013 #13
    Oh well then, thanks for the help.
     
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