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Node voltage method

  1. Sep 7, 2014 #1
    1. The problem statement, all variables and given/known data

    Use the node-voltage method to find v0 in the circuit below.

    2. Relevant equations

    i1+i2+...in=0
    i=v/R

    3. The attempt at a solution
    So I set my reference node to the top of the middle line(above 25Ω)
    Equation...
    24V/(20+80)Ω+v0/25+.004A=0

    Now I can solve for v0=(-.004-24/100 )* 25, v0=-6.1V

    I think I did something wrong, I'm confused about a few things. How do I know where to take my reference node? Also, I'm solving for v0, yet I'm adding .004 amps to the answer. Since I'm solving for voltage, how is this possible?

    Edited:Uploaded picture
     

    Attached Files:

    Last edited: Sep 7, 2014
  2. jcsd
  3. Sep 7, 2014 #2

    ehild

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    I do not see any figure.

    ehild
     
  4. Sep 7, 2014 #3

    ehild

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    that is not correct. The current through the 20+80Ω resistors flows through the potential difference v0-24V.

    ehild
     
  5. Sep 7, 2014 #4
    Oh I see. I updated my solution:

    (v0-24)/100+v0/25+0.004A=0

    v0/100Ω+v0/25Ω=24V/100Ω-0.004A

    0.05v0=.24A-.004A

    v0=4.72V
     
  6. Sep 7, 2014 #5

    ehild

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    It is much better, but 40 mA=0.04 A.

    ehild
     
  7. Sep 7, 2014 #6
    Okay, I fixed it. v0=4.00V. Thank you.
     
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