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Homework Help: Could Somebody help me please? EMF in parallel

  1. May 13, 2004 #1
    Ok, the question says: "Find the magnitudes and directions of the current through the 22 ohm and 15 ohm resistors (the internal resistance of the batteries is negligible)"

    My question is how do i determine this if there's a second emf in the problem?

    here's a picture of the problem:
    picture

    i tried using Kirchoff's loop law at first, first determining these two formulas:
    0=E1-I1R1-I2R2
    =9.0 - 22I1 - 15I2
    I1 = .41 - .68I2

    and

    0=E2 - I2R2
    = 6-15I2
    I2 =.40

    The problem is the second equation doesn't incorporate I3, so i cant use I3 = I2 + I1, so I'm stuck here.
    Then I thought about using Ohm's law, but I am not sure how do i use E1 in terms of the parallel circuit to determine the total current going through the whole circuit. Please help me someone :smile:
     
  2. jcsd
  3. May 13, 2004 #2
    by the way, the directions for I1, I2, and I3 in the picture are my predictions on the current flow throughout the circuit
     
  4. May 13, 2004 #3
    bump, please help me =(
     
  5. May 13, 2004 #4

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    I'm no electrical engineer, but...

    It seems to me that given your choices for current flow (and I am presuming you are using conventional current, which imagines that a positive charge is what is flowing), your first equation has a bogus sign and should be:

    0=E1-I1R1+I2R2.

    Does it help to write another equation based on the third path of flow? That is the one with the two batteries and R1 in it:

    E1+E2=I1R1.

    That would allow you to immediately solve for I1. Then You could put that value in my corrected version of your first equation and solve for I2.
     
    Last edited: May 13, 2004
  6. May 13, 2004 #5
    so there would be no I3?
     
  7. May 13, 2004 #6

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    If my analysis is correct, then it gives you I1 and I2, and as you said, you can then get I3 by adding those two: I3 = I2 + I1.
     
  8. May 13, 2004 #7
    alright, thank you so much for the help :)
     
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