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Circuit Problem with Kirchoff's rules (ugh)

  1. Aug 12, 2011 #1
    1. The problem statement, all variables and given/known data

    Determine the current in each branch of the circuit shown (here:)
    [PLAIN]http://img811.imageshack.us/img811/5084/physicschapter2817.jpg [Broken]

    2. Relevant equations
    Kirchoff's rules, I think is (and I'm probably looking at it wrong):

    summation of ΔV around closed loops is 0,

    summation of current at any junction is 0

    (Current) = ΔV / (Resistance), etc

    Resistors connected in series = (R1 + R2 +...), etc

    3. The attempt at a solution
    The red spike lines are resistors.

    I am just totally stunned here. This problem got to me to the point of me having to put it here and to draw it in MS paint, and sorry if it looks like an ugly drawing...

    Anyway the only thing I can do right now is to just simplify the resistors first. Two of em are connected in series so the resistors on the right are simplified to 4 ohms and the ones on the middle line become 6 ohms.

    It seems very hard to apply Kirchoff's rules at all and I am not sure how to do apply Kirchoff's rules here. Also I am not sure on what the problem means by "each branch of the circuit. And with the batteries it's even more confusing.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Aug 12, 2011 #2


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    Science Advisor
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    Gold Member

    Two pairs of resistors can be simplified (which ones?) To start this problem, you need to draw currents in each branch of the circuit and label them i1, i2 etc. Assume a direction; if your assumption is incorrect, when you put in the numbers the currents will be negative. For this circuit you will need two sum of voltages equations and one sum of currents equation.

    For future reference, you can draw resistors as skinny rectangles and if you label each as as a number followed by Ω (or "Ohms"), everyone will know them for what they are.
  4. Aug 14, 2011 #3
    I think I may want to know how to make summation of voltages equations and that's probably where I'm having trouble.

    I'll get other help from this in the meantime and check back in.
  5. Aug 14, 2011 #4


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    Staff: Mentor

    Here's your circuit redrawn with the simplifications that you've already described.


    There are three branches. I've also labelled two of the nodes as "a" and "b", and we can assume that node "b" represents a common reference point (designated here by the circuit "ground" symbol at node b).

    Suppose for the sake of argument that you happened to know the voltage (with respect to node b) at node a. Call it Va. Can you mark the diagram with currents for each branch and then write KVL equations for those currents for each of them using Va?

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