Circuit Sudoku

During this semester, which mostly consists of electricity and magnetism, I’ve really started to appreciate that the content is the vehicle through which students develop problem solving, critical thinking, and long-chains of reasoning. Later I will write how electrostatics is a great start to developing these long-chains of reasoning before we really exercise that skill with circuits. While not as challenging, circuit analysis is a good application of problem solving skills that illustrates how organizing data can make it much easier to solve problems.

We’ve started calling this problem-solving approach Circuit Sodoku.

The technique has evolved over the years based on input by teachers and students. I expect that it is similar to techniques used elsewhere. Regardless, my students find it very helpful when analyzing complex circuits.

At the heart of the technique is the V = IR table which has the following elements described below and illustrated in the photo of a group’s whiteboard:
* three columns: V (voltage), I (current), and R (resistance)
* the first row represents the equivalent circuit which specifies the voltage of the source, the current through the source, and the equivalent resistance of the circuit.
* each subsequent row corresponds to a resistor in the circuit

Students follow these steps to analyze circuits:
1. solve for the equivalent resistance (redrawing the circuit after each step, if necessary)
2. calculate the current through the supply based on the supply’s voltage and equivalent resistance
3. look for resistors in series or parallel with the source and update the table with the current or voltage associated with that resistor
4. apply the loop rule and junction rule to complete blanks in the table

Whenever two of the three columns for a row are completed, students use Ohm’s Law to calculate the third value.

Here’s an example:

circuit whiteboard

Just to be clear, Circuit Sodoku is not the heart of our circuits unit. Before we start analyzing circuits in this manner, we have spent weeks developing our conceptual understanding of circuits using the [CASTLE curriculum]( Many students find Circuit Sodoku a welcome break at the end of the unit.

Circuit Sodoku used to be the most challenging problem-solving application of my circuit unit. Now it is the easiest. I’m pleased we are focusing more on developing these essential problem solving, critical thinking, and long-chains of reasoning skills.

4 thoughts on “Circuit Sudoku

  1. Tony

    It was so funny to run across this post in my feed reader- I thought for a second, “Did I write this and forget about having done so?” I used a very similar technique with my students, calling the problem-solving process “Circuitoku.” Keeping one of those V=IR tables, the hardest part I flux was to stress the importance of redrawing the new circuit after finding equivalent resistances. So many students wanted to combine multiple sets of resistors simultaneously (which is fine, really), though they would inevitably get turned around upon making the judgement to retain the current or voltage drop later on in the process. Making into a “game” seemed to help kids engage in the “fun” of the problem.

    I’ve been meaning to write a little series on this section of the curriculum for quite some time- reading your post has inspired me to start. If I write a “Circuitoku” post, I’ll be sure to leave the link for it here.

    1. geoff Post author

      I too struggle to convince students to redraw the circuit as they combine resistors. As you can see, this group didn’t on their whiteboard. Sometimes I think students are worried about running out of graphite or paper when it comes to writing and drawing intermediate steps!

      Please do leave a link to your posts when they are written!


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