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Homework Help: Kirchoof's rules problem

  1. Mar 11, 2008 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    The change in Voltage = 0.

    3. The attempt at a solution

    Ok I have no clue where the loops go from. I want to say something like the current for I1 starts at the 10V battery in the middle and the current would look something like this:

    8ohm + 2ohm +15v +I1 +3ohm - I2 = 0.....

    I just really don't understand these problems and could use some help thanks.
  2. jcsd
  3. Mar 11, 2008 #2
    First, making use of Kirchhoff's first rule :
    The algebric sum of current at a junction is zero.
    We have I3 = I1+I2.
    Then , by considering two loops of the circuit,(there are a total of three circuits, choose two you like)

    Setting up equation
    20-10I3-I1(2)+15-3I1-4I3 =0

    and solve it.
  4. Mar 11, 2008 #3
    Thanks, so do I just do substitution from there?
  5. Mar 11, 2008 #4
    and I3=I2+I1.
    all currents are solved
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