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Homework Help: Kirchhoff's Laws

  1. Jan 18, 2014 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    [tex]\sum I_{in} = \sum I_{out}[/tex]
    [tex]\sum \epsilon = \sum pd[/tex]

    3. The attempt at a solution

    Can anyone identify any mistakes in these? Probably signs

    [tex]I = I_1 + I_2[/tex]
    [tex]12=4I_1 +3I[/tex]
    [tex]5=4I_1 - 2I_2[/tex]
  2. jcsd
  3. Jan 18, 2014 #2


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    Science Advisor
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    2017 Award

    What lets you think there are any mistakes ?
  4. Jan 18, 2014 #3
    The answers have I1 and I2 with opposite signs. I get them both as positive.
  5. Jan 18, 2014 #4


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    Staff: Mentor

    I make all currents positive for the directions shown.

    I'm not sure what is achieved by that + sign accompanying each current arrow? It seems superfluous if it duplicates the function of the arrowhead, and just clutters the diagram.
  6. Jan 19, 2014 #5
    Well that's good news. And, yeah, I guess it's just intended to help with the maths side of things.
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