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Homework Help: A Kirchhoff's Law Circuit Analysis Problem

  1. Feb 26, 2009 #1
    1. The problem statement, all variables and given/known data
    If R=1.29×103 Ω and ε=239 V, determine the magnitude of the current in the horizontal wire between a and e.

    http://img10.imageshack.us/img10/3746/sbpic2823.png [Broken]

    2. Relevant equations
    Kirchhoff's circuit laws.

    3. The attempt at a solution

    I'm having trouble mostly with getting this thing started. The problem I'm having is that I don't know how to properly figure out what the directions of the current throughout the circuit are.

    I checked with a simulation program, and it tells me all the directions go like this:

    http://img10.imageshack.us/img10/4135/sbpic.png [Broken]

    I don't understand how I'm supposed to predict that though...

    I'm also having trouble establishing the voltage loops in the circuit. If the current is considered the way it is above, doesn't that mean that I can't use the exterior rectangular part of the circuit as one loop?

    If someone could help guide me through this a little, or at least get me started on the right path, it would be very helpful. I'm normally pretty good at physics... but this circuit analysis thing is through me off a bit... maybe I just really suck at electricity :p.

    Also, if anyone knows of any good resources (i.e. Youtube videos or other websites) for learning this stuff with guided examples, could you sent the link? The only videos I've been able to find so far are with ridiculously easy examples only containing one battery and a couple resistors.

    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 26, 2009 #2
    You don't need to predict the directions of the currents. You can determine the direction from the sign of your answer, if its negative the current is flowing to the opposite direction of what your arrow shows. And this question is quite easy, if you calculate the currents of both supplies separately. So change one of the voltage supplies to a short circuit and calculate the current between a and e. The do the same for the other supply and sum the two currents.

    Btw: Nice username!
    Last edited: Feb 26, 2009
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