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Node Voltage Method

  1. Feb 3, 2016 #1
    1. The problem statement, all variables and given/known data
    Find the voltage, V, across the 6A current source

    2. Relevant equations
    V=IR
    Node Voltage Method

    3. The attempt at a solution
    Did I set this up correctly to find my voltage?
    Screen Shot 2016-02-03 at 1.34.06 PM.png
     
  2. jcsd
  3. Feb 3, 2016 #2

    gneill

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    Staff: Mentor

    Almost. Be careful of the signs of the terms.

    Judging by the sign you gave to the 6A supply term you're summing currents leaving the node. So why are your last two terms negative?
     
  4. Feb 3, 2016 #3
    Oh, woops. Read the polarities incorrectly. So if I change the last 2 to positive, it's good?
     
  5. Feb 3, 2016 #4

    gneill

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    Yes, that would be a correct expression. Make it an equation by setting it equal to zero :smile:
     
  6. Feb 3, 2016 #5
    Thanks!!!
     
  7. Feb 3, 2016 #6
    Got stuck again! :nb) The next question asks "What is the power associated with the 10V source?" I can find it using P=IV=I^2R=V^2/r, but how do I find the current through the 10V source?
     
  8. Feb 3, 2016 #7

    gneill

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    Staff: Mentor

    Each term in the node equation represents a branch current. One of the terms corresponds to that current. Pick it out and use it now that you've found the node voltage.
     
  9. Feb 3, 2016 #8
    Ohh. So I use (Vx-10)/20= (36-10)/10 = 2.6A And then using P=IV I can do (2.6A)(10V)= 26W***?
     
    Last edited: Feb 3, 2016
  10. Feb 3, 2016 #9

    gneill

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    That would be the idea, yes.
     
  11. Feb 3, 2016 #10
    Ok thanks!! 13W***
     
  12. Feb 3, 2016 #11

    gneill

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    Check your calculation for the current. (36 - 10)/10 = ?
     
  13. Feb 3, 2016 #12
    Woops! 26 watts. :confused:
     
  14. Feb 3, 2016 #13

    gneill

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    Try again. Show your calculations.
     
  15. Feb 3, 2016 #14
    What? Where did I go wrong? I = (36-10)/10 = 26/10 = 2.6A. Using that current and P=IV I can find the power in the 10V source. P = (2.6A)(10V) = 26 Watts
     
  16. Feb 3, 2016 #15
    ORIGINAL QUESTION: what is the power associated with the 10V source?
     
  17. Feb 3, 2016 #16

    gneill

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    Staff: Mentor

    Ah. My mistake. Sorry. I was thinking of the power associated with the branch as a whole. You have the correct result.
     
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