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Kirchhoff's voltage law problem: Batteries, switches, resistors

  1. Apr 23, 2016 #1
    1. The problem statement, all variables and given/known data
    擷取.PNG
    for S1,S2,S3,S4 are all closed at the long time
    find the current in each resistor
    2. Relevant equations


    3. The attempt at a solution
    why I3 is not = i2?
    the solution of this question is
    24-28I1-I212-12=0
    7I1-32=3-----(1)

    12-12I2-163=0
    3I2+43=3 ---(2)

    I1+I2-I3=0---(3)

    I1=0.492 I2=0.148 I3=0.639

    why there are 3 current in 2loop and I2 is not =I3 and why at the top loop
    the equation is not 24-28I1-[I1-I2]12-12=0???
     
  2. jcsd
  3. Apr 23, 2016 #2

    andrewkirk

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    Science Advisor
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    Currents are measured through wires, not in loops. There are three wires through which different currents are flowing (ignoring the wires with negligible resistance), so we measure three currents.
    Because the currents going out rightwards from the top two wires return leftwards in the third wire.
     
  4. Apr 23, 2016 #3
    Thank
     
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