The first-year students are solving series circuits and explaining what’s happening.  Most are able to connect their answers and thoughts to evidence we’ve gathered this semester.  But most are struggling with the questions about causality.

For each effect they describe mathematically, I ask them to explain what is physically capable of causing that effect. Or, they can choose to explain why the result seems like it can’t be happening.   It doesn’t have to be cannonical, but it must be internally consistent, not circular, and supported by our evidence.  They are struggling most with explaining Kirchhoff’s Voltage Law.  This is understandable — I don’t think I could explain it heuristically either.  However, only one student took the opportunity to say why it doesn’t make sense.

We’ve done lots of practise writing cause statements.  They know what “begging the question” means.  I’ve modelled, and we’ve practised, the importance of saying “I don’t know” when that’s the most accurate thing we can say. Examples of student thinking are below.

I’m tempted to propose a taxonomy of acausal strategies.  Which examples of student thinking do you think fit where?  Would you add or remove categories?   Could you propose some pithy names for them?

  1. It does that because it’s designed to do that
  2. It does that because if it didn’t, this other important thing wouldn’t happen
  3. It does that because there’s a law that says it has to do that
  4. It does that because it does that (begging the question)
  5. It does that just because

My questions are:

“An electron has to use up all its energy that it gets from the battery.  This is caused because if all of the energy wasn’t used, the circuit wouldn’t give accurate results, or work properly.”

“When electrons pass through a component, that causes them to lose energy.  The electrons would have to be able to flow through the circuit in order to keep the current and battery functioning.”

“An electron has to use up all the energy it gets from the battery.  This is caused because if the voltage from the power source is 5V, the electrons have to use up all of their energy, in this case they use up all of it in the resistor (except for the little energy used in the switch).”

“The electrons always use up exactly the energy they gain in the battery because of conservation of energy.”

“It doesn’t make sense that if there’s only one component in the circuit, it always uses up exactly the battery’s voltage.  A higher resistor should be like a steeper hill — harder for the electrons to get past, and requiring more energy.”