While students might be perfectly able to calculate complex electric circuits using Kirchhoff's laws, they frequently fail to solve apparently much simpler conceptual problems involving circuits with just two or three light bulbs and a battery.1 McDermott and Shaffer found that one of the problems is that students conceptualize the battery as a constant current source rather than a constant voltage source.2 To help students confront this common misconception, we present some experiments and concept questions with an actual constant current source.

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