Explaining Magnetism

An email I received today:
First of all let me introduce myself… I am just finishing up my first year as a Physics teacher. I have come across a situation that I am a little bit stuck on trying to explain. I have been going through Electricity and Magnetism. Well, I should say that I have already taught this, but am now reviewing for the final exam, and I am coming back up to explaining what causes magnetism. I just don’t feel like I explained it clearly enough. When I try to explain Orbital magnets as well as Spin magnets I seem to struggle being clear in my explanation; how would you go about trying to explain this to High school seniors? If you could offer an explanation I would appreciate it. I am still trying to wrap my head around being clear in my explanations. I did not go to school for Physics; I did take a couple of classes and that qualified me to teach it. I want to be the best teacher I can be so that is why I am asking for some help. Once again I appreciate you taking the time to answer my questions.

My *way too long* of a response:

Thanks for the email. Congratulations on making your way through your first year teaching physics!

You’ve really opened a big issue, not only about magnetism, but about the nature of explanation and learning. My first suggestion in making progress through the big issue would be to watch and mull over this commentary by Richard Feynman, which is both about the nature of explanation and the nature of magnetic forces: http://www.youtube.com/watch?v=MO0r930Sn_8

I’d love to talk about the video. For me, the biggest issue in teaching is not having the best explanation, but in understanding the ways in which my students are going to come to learn new things from the things they already know. That means I need to know a lot about how they already think, understand things, and even how they come to settle upon things as being true or not. Only in this way can I know what the best explanation might look like for them. And at the end of the day, we have to pursue that explanation together.

Magnetism is notoriously funny. Some teaching physics friends of mine refer to “magnetism” as “turtles all the way down”. It’s a joke, but also true. Big magnets are made up of mid-size magnets, and those mid-size magnets are made of magnets that are tiny… and those made up of ones even tinier…and those magnets are made up of particles that are magnetic, those are made up of sub atomic particles that are magnetic. Starts to sound ridiculous, that our best explanation of magnets is that magnets are made up of magnets… but that’s all we have really.

Of course, when tiny magnets work together, they can produce magnetic effects that are larger, or when not working together, they produce tiny or no magnetic effects. Why are those tiny things magnetic? I don’t really have good explanations for those things. But understanding that there are magnetic things, and that they can push and pull and twist on each other, and that they can arrange themselves in ways that amplify those pushes and pulls is pretty much everything to know. Then the devil’s in the details of figuring out what arrangements lead to what kind of effects. The really specific details are the tough work of undergraduate and graduate physics.

If you watched the video, you’ll see that Feyman’s point is that also that magnetism is not meant to be explained -it is meant to do the explaining. That’s a stance that he is taking–magnetism is a powerful idea to explain other things. The story of how we have come to accept magnetism as a true and worthwhile idea is really curious.  I know I probably haven’t satisfied your question, but it’s the best I can do.

What would you have written?


One thought on “Explaining Magnetism

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  1. What my students really asked: “Yeah, ok, magnetic stuff is made of magnetic domains. But what causes the domains to be magnetic?” What I really have said to students: “I don’t understand it fully either. If you feel like that stuff in the textbook about ‘magnetic domains’ is avoiding the issue of what causes this, I agree and I’m proud of you for noticing.” It interests me that your correspondent seems to be taking the approach that he understands it but can’t explain it clearly, while you’re taking the approach that you don’t fully understand it. I want to understand more, someday, about how people decide which one of those two responses to use.

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