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Homework Help: Finding Currents in a Circuit

  1. Jan 15, 2012 #1
    1. The problem statement, all variables and given/known data
    Find currents I1-I6. I'm really looking only for the equations though...

    2. Relevant equations

    3. The attempt at a solution
    I tried to set up equations for the nodes and loops:
    Node a:[tex]I_2-I_6-I_3=0[/tex]
    Node b: [tex]I_3+I_5-I_1=0[/tex]
    Node d: [tex]I_1-I_4-I_2=0[/tex]

    Loop 1: [tex]-V_1+I_1R_1+V_2+I_5R_2[/tex]
    Loop 2: [tex]-V_2+I_2R_5+I_6R_4[/tex]
    Loop 3: [tex]I_3R_6-I_5R_2-I_6R_4[/tex]

    I'm pretty sure that the above equations are not correct since I was not sure how to incorporate R3 and I am also a little bit confused about how to relate I1 and I2 and I4.

    Thanks for the help!

    Attached Files:

  2. jcsd
  3. Jan 15, 2012 #2


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    Staff: Mentor

    Your node current equations look fine, except that you seem to have interchanged nodes a and d.

    For your loops, they need to be in the form of equations (there should be an "=" in there somewhere). For loop 1, treat R3 as you did the other resistors; there's a voltage drop across R3 due to the loop current i1 flowing through it.
  4. Jan 15, 2012 #3
    Yeah I meant to equal all the loops to 0. How about this:
    Loop 1: [tex]-V_1+I_1(R_3+R_1)+V_2+I_5R_2=0[/tex]
    And you are right about the nodes a and d.. They are switched in my diagram on paper.. thanks!
  5. Jan 15, 2012 #4


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    Staff: Mentor

    Yup. That looks okay.
    You're welcome :smile:
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