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Homework Help: Finding Unknown quantities in a circuit

  1. Jul 10, 2016 #1
    1. The problem statement, all variables and given/known data
    See attached photo
    2. Relevant equations

    Kirchhoff's current law

    3. The attempt at a solution

    So, I was solving for I3 and got the correct answer, but I want to be sure that I arrived at the right answer by using a reliable thought process. I dont wanna get lucky!

    So, I had already determied I1 and got 1A.

    With that information I thought... It starts out with 2 A, and there are 2 identical resistors (R2 and R3). I3 = 1 A, so these 2 resistors must each have a current of .5 A going through it. From that I found that I3 = .5A

    Is this a reliable thought process? What are some other ways to view this problem?


    Attached Files:

  2. jcsd
  3. Jul 10, 2016 #2


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    Homework Helper
    Gold Member

    Your method is correct. I believe it is the only way to solve this problem.
  4. Jul 11, 2016 #3


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    Staff: Mentor

    Any solution is going to rely on Ohm's and Kirchoff's Laws.
    But you could use the fact that R1 is dissipating 30W to find ##\left(\sf using~\color{blue}{power﹦\frac{E^2}R}\right)## that E=30V

    Then, with the battery delivering 30×2=60W, this means the R2 R3 combination is dissipating 30W. So R2##\|##R3 must be 30Ω, and so on ....
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