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Kirchoff's Law - Supernodes

  1. Aug 16, 2014 #1
    Hello All,

    I am trying to teach myself basic EE. The textbook I am using gave the following example:

    1. Find IS2. Diagram is attached.
    IS1 = 2A
    I2 = 3A
    I3 = 2A
    I4 = 1A
    I5 = 0A

    The answer in the textbook is 1A.

    My Method using KCF:
    IS1 + IS2 - I2- I3 - I4 -I5 = 0

    Substituting the numbers I get: 2 + IS2 - 3 - 2 - 1 = 0; IS2 = 4A

    I am not sure where I am going wrong here.

    Thanks for any insight!

    Attached Files:

  2. jcsd
  3. Aug 16, 2014 #2


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    Staff: Mentor

    At the junction of R1 and R2 applying KCL you see:
    Is1 + Is2 = I2

  4. Aug 16, 2014 #3


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    Staff: Mentor

    If you look at the equation for the supernode, it won't involve IS2
    current in = current out

    Is1 = I3 + I5

    Good luck with your studies.
  5. Aug 16, 2014 #4
    Ahhh. Thanks NascentOxygen!
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