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Basic DC Circuits - Kirchoff's Rules Lab questions

  1. Feb 22, 2014 #1
    1. The problem statement, all variables and given/known data
    I need to come up with a formula to solve for i2 given the diagram of the circuit attached. I can identify 2 junctions and 3 loops.

    2. Relevant equations
    *The algebraic sum of the currents into any junction is 0. By convention the currents entering the junction are positive and the currents leaving the junction are negative.
    *The algebraic sum of the potential differences in any loop must equal 0.

    Junction B: i1-i2+i3=0 (Eq.1)
    Junction E: -i1+i2-i3=0 (Eq.2)
    Loop ABEF: ε1-i1R1-i2R2=0 (Eq.3)
    Loop BCDE: ε2-i3R3-i2R2=0 (Eq.4)
    Loop ACDF: ε1-i1R1+i3R32=0 (Eq.5)

    3. The attempt at a solution
    Here is where I run into trouble. I am having difficulty using the above equations to find a formula for i2. I am not sure if the equations above have an error in them or if I am heading in the wrong direction. I need to get everything in terms of R1,R2,R3 and ε. In the experiment ε1 is a fixed power supply and ε2 is a variable power supply. I am assuming we can add and subtract them and get:
    ε1-1R1+i3R32=0 → -i1R1+i3R3=0
    But I cannot seem to work the equations well enough to get everything in terms of Rx, i2 and ε so like I said I think there is an error above. I am also not very comfortable working with systems of equations.

    Attached Files:

  2. jcsd
  3. Feb 22, 2014 #2
    Have you tried using Woflram Alpha (or similar programs) to solve them? That could help you to find out if you stated the problem correctly. I can help you if you don't know how to use it.
  4. Feb 22, 2014 #3
    I have used Wolfram to solve some simple systems of equations involving x and y. I am not sure where to begin with something like this.
  5. Feb 22, 2014 #4
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