A Physics Fairy Tale

Once upon a time, in a magical Physics kingdom, there lived an evil teacher who gave resistor network problems like this:

The Evil Physics Teacher made his students solve all kinds of complex resistor networks.  It was time consuming, but the Evil Teacher thought it was worth it because it proved their ability to manipulate Ohm’s law, Kirchoff’s laws, and the resistor formulas.

And the one day, a student asked a simple question:

“What does this circuit do?”

The Evil Physics Teacher paused, and then somewhat sheepishly admitted that the resistor network didn’t actually do anything.

“Can you show us a resistor network that does do something? Like one that an electrical engineer would actually design for something?”

Again, the teacher paused. Um, no. He explained. Everything has resistance, so it is important to be able to figure out total loads, but no one actually designs resistor networks, per se.

“But like, in a house everything is in parallel, right? So current loads would just be the sum of individual currents. Nothing is ever in series in a house.”

The teacher thought about that, but did not reply. Instead, at the end of the day he went home to ponder. Perhaps, just perhaps, there was something to this thought. Resistor networks did allow students to exercise their understanding of electricity, but in an overly complex, unrealistic and – let’s face it – borderline sadistic way. And so the Evil Physics Teacher mended his ways. He began providing simpler questions that still exercised the same skill sets without consuming a full period for a single problem.

As a result, learning the material was quicker and more readily attainable, and there was more time to move onto richer and more exciting things in the curriculum.

And they all lived happily ever after.

(PS – some parts are truer than others…)


4 thoughts on “A Physics Fairy Tale

  1. Andy Rundquist

    I really like to give them a table similar to what you have at the bottom right, but on tests I’ll fill in one number and then ask them to fill in the rest. By giving one number, they don’t have to solve n equations with n unknowns, but rather they can start to say things like “if I know that, then I know this, and then . . .”. I really like it since I don’t like my tests to be about algebra skills. What’s really cool is having them tell it like a story (or at least order their answer in the order they found them) so I can see how they thought about it. One caveat: Make sure the number you give is correct. One time I was in a hurry and I convinced myself that any number would do. Wrong!

  2. John

    I like this fairy tale a lot. Why is it that students are asked to solve crazy networks like the one above, and never asked to calculate the equivalent resistance of their house, or what happens to this resistance when they turn on the washing machine? It seems like thinking about these questions would lead to much deeper understanding than figuring out whether R12 is in series or parallel with R5.

  3. Rick Fletcher @TRFletcher

    First of all, love the blog. I just found it. This example, I believe, demonstrates another aspect of our teaching craft you did not mention. I understand that teachers come in all flavors – from forced into a spot to the full-on practicing science professional. The deeper we know our field, the easier it can be to create practical lessons. I’m a PhD chemist by education and although it is a challenge, I can usually come up with a practical example of a concept on the fly. I imagine this is much harder the fewer college hours one has under her belt. Actually, I know this is true because I taught secondary science immediately after completing my BS in chemistry and I searched the textbook for applications every night just like the majority. So how can those of us with more practical experience help those with less practice? Can we develop curriculum? Can we provide summer experience? Can we be in more secondary classrooms? Can we provide more access to our years of practice using web tools like Skype or Elluminate? What can *I* do to help high school teachers make their classrooms more practical, and in turn, more interesting? Let me know your ideas. I develop programs. @TRFletcher on Twitter. fletcher@uidaho.edu


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