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Homework Help: KVL/KCL with two sources - can a loop have both sources?

  1. Jul 16, 2017 #1
    forum question.jpg
    1. The problem statement, all variables and given/known data
    In the circuit shown, find (a) the current in each resistors (b)The power dissipated in each resistor.

    2. Relevant equations
    V=IR, P=VI, KVL and KCL

    3. The attempt at a solution
    See attached.

    I was going to post this in the main section as its really a question about whether you can have two voltage sources in your equation, but I read the sticky on the main page for general physics and it directed all coursework type questions here.

    In the drawing I have a section underlined. When I set up my equations, I got two voltages in the equation. I wanted to know if that is valid? If I should come across another equation like this, is there a rule for knowing not to do this? The solution to this problem is not the same as what I derived. Please give me some direction with this, thanks!
  2. jcsd
  3. Jul 16, 2017 #2


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    Staff: Mentor

    Sure, a given loop can contain zero or more sources. For KVL their potential changes sum just as you've done.
  4. Jul 16, 2017 #3


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    Gold Member

    Your second equation is incorrect.
    There should be i2 instead of i1.
  5. Jul 16, 2017 #4
    Thanks mate! BTW - if you haven't seen the finale.... jumping the shark abit... Still a fan though :-)

    Hi CNH, I think I see the error now. The 5I1 should really be just I1 times the 1 ohm resistor. That makes it all work.
    Thanks gents!
  6. Jul 16, 2017 #5


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    Staff Emeritus
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    OP has 3 individual currents, each one for each branch of the circuit. He then uses a junction equation to relate them.
    Last edited: Jul 16, 2017
  7. Jul 16, 2017 #6


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    It was almost 12 am when I posted it and I was kinda sleepy:oops:. I guess I have to sleep now before I post anything stupider.
    Yes. I wasn't able to delete that because of network problems (I am traveling in a hilly area).
    Fixed it now.
    Last edited: Jul 16, 2017
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