# Finding Unknown quantities in a circuit

1. Jul 10, 2016

### Josh225

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!

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?

Thanks!

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2. Jul 10, 2016

### cnh1995

Your method is correct. I believe it is the only way to solve this problem.

3. Jul 11, 2016

### 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 ....