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2 Unknown Currents, 1 Unknown emf, and a little confusion to boot!

  1. Jul 10, 2009 #1
    (Solved.) 2 Unknown Currents, 1 Unknown emf, and a little confusion to boot!

    First off, hello everyone! I just formally joined the forums today after reading discussions from the shadows for a while now.

    This summer I'm taking the second part of a 200 level physics course and the homework (submitted online through the university) has gotten a bit a head of where we are in lectures. Normally it hasn't been a issue, but this particular problem has given me a headache.

    I've attached a fairly simple circuit, and the problem is to find I1, I2, and the value of the unknown emf.

    So far I've set up three equations to describe the circuit:

    1.) I2 = 2.40A - I1
    2.) Loop 1:
    5 ohm * (2.40A) + E - 2.0 ohm * I2 = 0​
    3.) Loop 2:
    -6.70 ohm * I1 - 15V + 5.0 ohm * 2.40A = 0​

    From there I've combined what I could in terms of multiplying the ohms and amps to give me volts in the equations, but no matter where I go from there I'm having difficulties setting up any further equations that will help me solve for the unknowns. And when I do manage to get one variable defined in terms of the others, I'll get something like amps for the unit of the unknown emf, so clearly something isn't right in my set-up, but I'm not sure what exactly.

    Any help that anyone can give would be mightily appreciated. Thanks in advance.

    Never mind all of the above. I realized I was making this problem out to be something much more difficult than I needed to, and was going about it all wrong. I got it figured out now!
    Last edited: Jul 10, 2009
  2. jcsd
  3. Jul 11, 2009 #2


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    Welcome to PF!

    Glad you got it, and thanks for letting us know (not everybody does that).
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