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Homework Help: Kirchhoff's current law and nodal analysis

  1. Oct 12, 2011 #1
    Hello,

    I'm looking to work out the current at I in the following circuit using Kirchoff's current law and nodal analysis:
    [PLAIN]http://img853.imageshack.us/img853/4792/circuitgem.jpg [Broken]

    Using Kirchoff's voltage law (and loop analysis), I got a current of (35/22)A, but for the current law method I'm having problems.

    I obtained the following equations using Kirchoff's current law:
    4i1+2i2+4i3=5
    -4i3-2i4=-10
    and nodal analysis:
    -i2+i3-i4=0
    i1+i4=I

    But solving these 4 equations produces a value for I of 0, which doesn't make sense, let alone agree with the answer using the other method.

    Any help will be greatly appreciated.
    Thank you
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Oct 12, 2011 #2

    phinds

    User Avatar
    Gold Member

    I got as far as your first equation and have no idea how you got it. (Actually, I think I know, but it's nonsensical)

    Try drawing the I's and V's out on the diagram and writing equations that make sense.

    It's a VERY straightforward problem.
     
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