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Homework Help: Circuit analysis equations

  1. Dec 9, 2012 #1
    1. The problem statement, all variables and given/known data

    Alrighty, my question is the exact same one that is written in this post - https://www.physicsforums.com/showthread.php?t=528337

    The issue I'm having is understanding how to make/write my equations. I guess I just don't understand how you can know which way the current goes when you hit an intersection. I would LOVE it if someone could go through how they decided what the equations equal. I understand that you start at the battery (or at least I like to) and I usually move from - to + on the battery and then try to track the current but I get confused!! I would show you my photo of the current but I changed it a million times so it looks pretty weird.

    Anyways- Can anyone give me the super detailed, step by step?

    Thanks- Studying for exams :P

    2. Relevant equations

    P = IV
    V = IR
    Last edited by a moderator: Dec 9, 2012
  2. jcsd
  3. Dec 10, 2012 #2


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    As long as you are consistent with your notation it shouldn't matter which way you assume the current will go. If you define one way as +ve and your assumption turns out to be wrong the value you calculate will be -ve.

    Try defining the currents so that you can write I1 + I2 + I3 = 0 rather than trying to guess the direction and writing I1 + I2 = I3
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