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Battery Problem (finding current w/ batteries in parallel)

  1. Mar 11, 2007 #1
    1. The problem statement, all variables and given/known data
    Find the current flowing through the 200ohm resistor
    [​IMG]

    E1=5v
    E2=10v
    E3=15v
    r1=3ohms
    r2=6ohms
    r3=9ohms


    3. The attempt at a solution

    I know that I1+I2+I3=I
    I cant seem to get a loop rule that will allow me to solve for I though.

    I came up with the equivalant resistance in the three resistors equal to 1.6ohms.

    I tried to draw a simplified circuit diagram, but i am not sure how to do that with different voltages on batteries in parallel.

    thanks
     
  2. jcsd
  3. Mar 11, 2007 #2
    Equivalent resistance wont help. Youve got 4 unknowns and need 4 equations. Theres enough information to use one junction equation and 3 loops. Make use of the inner loops, and use a matrix to avoid algebra mistakes whenever possible
     
  4. Mar 11, 2007 #3
    i tried that and i seem to just keep proving that I2=I2, I1=I1, etc....
     
  5. Mar 11, 2007 #4
  6. Mar 12, 2007 #5
    I worked on the loop equations more and found I1, I2, and I3 in terms of I.

    I then substituted those into the I1+I2+I3=I equation getting a current (I) of .041 A leading to a deltaV of 8.1V.

    Does this sound right? The Current was .137A when connected in series and the deltaV of the 200 ohm resistor was 27.4V.

    Thanks
     
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