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Homework Help: Mesh-node analysis from a circuit

  1. Mar 28, 2010 #1
    1. The problem statement, all variables and given/known data

    http://img684.imageshack.us/img684/7530/meshr.jpg [Broken]

    2. Relevant equations



    3. The attempt at a solution

    I am pretty sure what I did below is wrong because R3 is negative... where did I go wrong?

    Left loop: 0.02
    Right loop: i3

    current through the bottom LED = (0.02 - i3)
    We want the top LED to pass the same amount of current.

    Top loop: R3(0.02 - i3) + 2 + 150((0.02 - i3) - i3) + 240((0.02 - i3) - 0.02) = 0
    0.02R3 - i3R3 + 2 + 3 - 150i3 - 150i3 + 4.8 - 240i3 - 4.8 = 0
    (0.02 - i3)R3 = -5 + 540i3
    R3 = (-5 + 540i3) / (0.02 - i3) (1)

    Loop i3: 110i3 -2 + 330(i3 - 0.02) + 150(i3 - (0.02 - i3)) = 0
    110i3 - 2 + 330i3 - 6.6 + 150i3 - 3 - 150i3 = 0
    440i3 = 11.6
    i3 = (29/1100) (2)

    From (1) & 2):

    R3 = (-5 + 540i3) / (0.02 - i3)
    = (-10160/7)
    = -1451.42 O
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
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