Can you analyze this circuit?

-May 06, 2014

My high-school freshman (grade 9) is studying basic circuits in physics class. She asked me for help with the following circuit.

Go ahead, solve for R1 and Ix.

Now it's been a few years since I studied basic DC circuits in school, but clearly, something's wrong here. How would you advise a ninth grade student on how to solve for R1 and Ix?

We all know that you can’t have more current in a branch of a parallel circuit than comes out of the battery, right? Could Ix be -2 A? Impossible. Well, not without another current source. I think it's safe to say that here is no implied current source in the right branch. Obviously, there's a typo where 12 A should be 2 A. Then it all makes sense because Ix must be 8 A given the 3-Ω resistor and the 24 V DC source. R1 is therefore 12 Ω.

What would you do if you were the teacher? I'd really like to see the teacher's edition of the workbook. It probably has the right answer, but who knows?

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