I posted a new podcast – “Ooh you make my motor run” on my Science Teaching Tips podcast.  One of the Exploratorium staff educators, Modesto Tamez, tells how he gets students exploring electromagnets, a great preparation for making an electric motor.

Here’s the Stripped Down Motor activity: www.exploratorium.edu/snacks/stripped_down_motor.html

[[AAPT SESSION: TRANSFORMING UPPER-DIVISION E&M I]]

This post is primarily for college physics teachers.

Hey, if you’re ever presiding over a conference session, here’s a tip for you. If one of your presenters has technical issues, don’t give her a hard time after the talk is over, even in jest, about having gone over time. Trust me. She’s already been beating herself up for it over the last half hour.

So, technical issues aside (and I tried four times to check my presentation on the conference computer prior to the session and was thwarted in some way each time, I swear!), my talk tonight went well. Here’s what I’ve been working on.

In our department, we’ve made a lot of changes to the freshman level courses, adding things like Tutorials and clicker questions and peer instruction that have been shown to improve student learning, because they get students really thinking about the material and engaged (and thus learning) instead of sitting passively and waiting for knowledge to be imparted upon them by the instructor. At the upper-division, however, there’s this sense that we need to stop “coddling” our students with these kinds of techniques, that we learned by lecture, so why shouldn’t they? If they’re not learning, maybe they should consider changing major at this point. But, I argue, that how you learn doesn’t suddenly change between the sophomore and the junior year, and we might do better by our students to try using some techniques that have proven effective at the lower division.

So, in our course we developed

  • Lists of what we concepts and skills we wanted students to learn
  • Homework questions that targeted those concepts and skills
  • A new assessment exam to see if we taught them those concepts and skills
  • New tutorials for teaching those concepts and skills
  • Interactive lecture techniques
  • Clicker questions

We found that when we compared students in a Traditional course to those who took a Transformed course, even though they were similar to one another coming in to the course, at the end of the course those in the Transformed course scored significantly better than those in the Traditional course on common exam questions and a conceptual exam. So, it worked! We can teach our majors better.

We’ve got all those materials on our website for other instructors to use.

And here is the Powerpoint of my talk (PDF) I’ve also got two posters — see the website above for those.

I just posted a new episode of my Science Teaching Tips podcast – Electrifying Ideas. My old boss, Paul Doherty, is a great storyteller, and this is one of the stories of science that he uses to explain the history of science. The ancient Greeks knew about magnets, and they knew about electricity, too. But it wasn’t until the nineteenth century that a connection between the two was discovered. Paul tells the story of how a professor made the connection . . . which led to modern motors.
Paul Doherty’s Web site

401px-drinkingstraws.jpgThis is a great little activity from Eric Muller’s While You’re Waiting for the Food to Come.

Get a plastic drinking straw, in its wrapper. Unwrap one end, so the straw is still wrapped in the paper, and then slide the wrapper quickly up and down over the straw, until the straw and wrapper feel a little warm.

Take off the wrapper and the straw will stick to the palm of your hand!

For extra fun, do this with a friend. Ask them first if they’re attracted to you or repulsed by you! Then both do the straw-thing, and hold the straws near one another (you’ll find that your friend is repulsed by you).

You can find a writeup of this activity on Eric Muller’s website.

Why does this work? The straw ends up negatively charged (it’s got just about 40 nanocoulombs of charge) after being rubbed with the paper. Since like charges repel, it will repel the other straw. And charged objects attract neutral objects, so it sticks to your hand.

This is the same principle as the old rub-the-balloon-on-your-head-and-stick-it-to-the-wall trick.

Here is a simulation you can play with that shows you the physics of this sort of trick.

I’ve created a couple posters of Maxwell’s Equations (differential and integral form) and you can buy them online at Zazzle, or just ask me to send you the electronic file and you can print them yourselves. Good for the junior level physics classroom.
Here’s a link to the integral form poster and to the differential form poster.

No post last week, as I was driving across the country from San Francisco to my new digs in Boulder CO. As I was camping in the middle of very very very dry Nevada, I noticed something a little cool. As any science teacher can tell you, any demonstration having to do with static electricity works best on a dry day (and is a terrible failure in, say, Florida). As I was rolling up my thermarest, I saw the tiny little grains of hay from the ground were sticking to it, and sticking straight out from it like little porcupine quills.

You can do this yourself with spices, like dill. Rub a plastic comb with a piece of wool, and hold it near dill and you can watch the dill dance in the electric fields. It may very well stick to the comb, too. The comb has grabbed electrons from the wool and is negatively charged. The dill has no charge, but when it’s brought near the comb, those negative charges push away the electrons on the dill, making the near end of the dill positive and the far end negative. It’s induced a charge on the dill. So, then the positive end of the dill sticks to the comb, and the negative end strains to get away, so you get the porcupine quill effect.

The same thing probably happened with my thermarest and the hay. The thermarest rubbed against the fabric of the tent, making one of them negative and one positive (I don’t know which, but if I had a tape electroscope I could have found out — I’ll write about that later). It’s easier to charge things like this on a dry day because water on the surface of things gets in the way of electrons jumping from one to the other.