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Parallel Emfs

  1. Nov 13, 2011 #1
    1. The problem statement, all variables and given/known data
    Calculate the current through the resistor of resistance for circuit B.

    Express your answer in terms of EMF, R1, and R2.

    http://imageshack.us/photo/my-images/163/screenshot20111112at110.png/"
    2. Relevant equations

    Kirchhoff's Loop and junction rules

    3. The attempt at a solution
    So I have these equations that I've figured out using Kirchhoff's Rules:

    There are two loops:

    EMF = I1R1 + I3R2
    EMF = I2R1 + I3R2
    I1 + I2 = I3

    I figured out pretty quickly that I1 = I2 by subtracting the top from the middle equation. I'm just not sure what to do next really...

    The answer I'm supposed to get to is I3 = (2EMF) / (R1 +2R2)

    I don't know why this is so confusing...but it is. So, assuming I did everything right, how do I get to the last (final) equation for I3?
     
    Last edited by a moderator: Apr 26, 2017
  2. jcsd
  3. Nov 13, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Make use of that fact to eliminate I1 (or I2) from either of the first two equations. Express I1 (or I2) in terms of I3. (Use your third equation.)
     
  4. Nov 13, 2011 #3

    BruceW

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    Homework Helper

    Simply use more substitution and rearranging to get the equation you want. You already have all the equations necessary, you don't even have to think about it anymore, just write out your equations (including your equation I1=I2), and then its just a problem of simultaneous equation solving.
     
  5. Nov 13, 2011 #4
    I think I'm super sleep deprived because that was pretty simple.

    Thanks you two :)
     
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