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Homework Help: Kirchhoff's Laws and Circuit Equation Help Request

  1. Mar 18, 2014 #1
    how do i calculate potential differences around the loops

    is i3+i4 equal to i5??

    this is actually from maths and i completely forgot how to do calculation around electrical circuits from physics

    could anyone please help me!!!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

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  3. Mar 18, 2014 #2


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    hi sozener1! :smile:
    hint: the eg top-right-hand corner is also a node, and has one current going in and one current going out

    sooo … ? :wink:
  4. Mar 18, 2014 #3


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    Note: Thread title changed to make it more descriptive of the thread content.
  5. Mar 19, 2014 #4
    actually you need only one more equation, since i1=i2, i3=i4 and i6 and i5 can be omited because they make no potential difference since they flow through short circuit.
    So the last equation is 0=i3 x R + i3 x R - i7 x R
  6. Mar 19, 2014 #5
    Hey there! It looks like this problem is just a use of mesh analysis without explicitly stating it.

    So, if you look at the loop of wire that has the voltage source connected to it in series, you know that the current in that loop of wire must be constant. This is a fundamental principle of current.

    What can you get from this? Well, it looks like i1 = i2 = i6

    Not only this, but on the strand of wire on the right, this same principle can be applied.

    If you use Kirchoff's voltage law around the first loop of wire on the left, you can see that:

    (Going in defined direction of current) = V+i1R+i7R = 0, also, I think they made a mistake or misused the notation, because the shorter side of a voltage source is supposed to be the negative end.

    From there, notice that i7 would have to be the net current between i1 and i3, and use the voltage rule around your second strand of wire in order to form another equation. After that, it is purely substitution, and assuming those R values are all equal, you'll have a nice result.
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