Dot Physics

Some quick comments on learning

I am totally ready to get back to blogging. In fact, I have a post that is 3/4th complete that I have been working on since before Christmas. Anyway, in order to procrastinate a little bit more I would like to share two learning observations (maybe they are not really about learning).

Kids these day

First, I was in the airport. When I am sitting around starring at the walls, I can’t help but accidentally overhear someone that is 4 feet away. So this guy was talking about how impressed he was with kids these day in school. They are learning all sorts of stuff that he had already forgotten. I can’t remember the exact topics, but the point I wanted to make: if you forgot it, did you really learn it in the first place? This is part of a theme that I have noticed in schools. It seems that memorizing stuff is a common task.

Random Magnet Question

The other question came from my niece – who is an extremely bright girl (not sure exactly what grade – maybe 5th). She was at home and didn’t have her science textbook, so she asked me the following:

“What happens to the electrons in a metal when it becomes a magnet”

I always worry about magnet questions because magnets are not that simple to understand at a fundamental level. Sure, there are some things you can do with magnets – especially if you want to do some experiments. However, asking questions like this or like “why can iron be a magnet, but not aluminum” to a 5th grader is like asking me how gravity works.

I am not sure that this is actually the question she was asking, but who knows. It is a bad question. The answer I gave her is this:

Suppose I take a piece of iron and rub it with a magnet so that it also becomes a magnet. During this, what happens to the electrons? I say nothing happens to the electrons. Why then does the iron become magnetic? The iron can be broken into “magnetic domains”. When the iron is acting non-magnetic, the domains are not aligned. This means that the magnetic fields of these domains sort of cancel. For iron that is magnetic acting, all these domains are aligned in the same direction.

She said she couldn’t find this answer online. And this is the second part of my rant. I think schools are training kids to just go look up silly stuff online. Don’t we already have google? Do we really need to train students to do this? Or are educators confusing looking up stuff with learning? Or are they just giving them busy-work?

Maybe the teacher just had the idea that magnets are just like electric charges – this is a common idea anyway. Ok – back to physics blogging.


  1. #1 meichenl
    January 11, 2010

    Hi Rhett,

    Understanding magnetism in everyday life is all about understanding electrons. It’s not that magnets are like electric charges, but that electrons are small magnets. Magnetic fields have some effect on nuclei, but in general that effect is small in comparison to the effect on the electrons, so that when you’re talking magnetism, you’re usually talking electrons.

    For example, a “magnetic domain” is a region in which the electrons’ spin states are aligned. So it’s not true that nothing happens to the electrons when iron becomes magnetized. The electrons’ spins become aligned globally in the piece of iron, rather than just locally in the small domains. This is a wonderful model system for teaching because it’s very simple, and if the student grasps it quickly, it’s easy to move on to discussing the concept of temperature and why heating the iron up will destroy the magnetism.

    Electrons have orbital angular momentum in addition to spin angular momentum, so the effects can be complicated. There are all kinds of crazy, interesting things that happen to electrons in a magnetic fields. In certain contexts, chemists know more about it than physicists because studying the way the spectrum of a molecule changes in a magnetic field due to splitting and whatnot provides significant information about the structure of the molecule.

    Imaging technologies like MRI also depend on what magnetic fields do to electrons. I’m sure there are many more examples that I don’t know much about.

    I also don’t understand the objection to having students look things up online. Understanding how to learn new things for yourself is an important skill for an adult, since we can’t possibly teach kids everything they need to know in school. This is a skill, and it should be taught. It takes time to learn how to distinguish which sources are credible, to learn how to cross-check what you read with different sources, to learn where to look for information and what to make of it when you get it. Children also have to learn what level of understanding they need at any given time – there’s a tradeoff between how well you can understand something and how much time and effort you put into learning it. You can’t just keep researching forever. Depending on the level of coverage you need, the way you search should be different. These are all things that kids have to practice, and a teacher can help them with it. Later on they’ll need other research skills, like documenting and citing their references and keeping and organizing notes for themselves. They’ll be able to learn these more effectively if they’re already comfortable with learning things online in a more relaxed context.

    I don’t really expect a fifth-grade teacher to have a good understanding of how magnetism works, so maybe it’s better for young students to learn how to make sense of a Wikipedia article than to be taught something incorrect by a teacher. It doesn’t necessarily mean the teacher’s being lazy. It might just mean they recognize their boundaries.

  2. #2 Jenny
    January 11, 2010

    Students do end up memorizing a lot of stuff in school. I hope that they actually understand it pretty well. However, we throw a lot at them in a pretty short time and there is no way it is all going to stick with them. That said, it’s possible that things they don’t truly remember (or don’t think they do) are still building a foundation for future learning.

    (I don’t know if this is making sense the way it does in my head. I have to rush to pick up my class from PE and I’m not getting my thoughts in order too well.)

  3. #3 Shawn Smith
    January 11, 2010

    Rhett, please turn close the <sup> tag. It’s getting really tough to read. Let’s see if this helps:

  4. #4 Rhett Allain
    January 11, 2010


    Sorry about that – I wasn’t paying attention. Fixed it. Thanks for pointing out my error.

  5. #5 Willy
    January 11, 2010

    When I taught high school science I tried to keep memorization out of it. I wanted the students to engage in higher level thinking, not just spewing definitions memorized so we could move on to the next chapter. Being able to take what seems like disparate information and ‘draw a line through the points’ was the goal I sought for my students. Even Einstein said, “never memorize what you can look up in books.”

    Most high school science is taught like history, with similarly disastrous results. Back in 1964 Richard Feynman told the AAPT to “teach the wonders” of science. They still haven’t gotten that message.

  6. #6 Shawn Smith
    January 11, 2010


    You’re welcome, and thanks so much for fixing that so quickly! On IE6, by the time the captions (Name:, Email Address:, etc.) for the entry boxes appeared, they were only a couple pixels high.

  7. #7 Alex
    January 11, 2010

    Yes you can talk about magnetism being a result of electron spins aligning but is there any chance that a 5th grader has any idea what spin is? I’m nearly through with a PhD in physics and I’m still not very comfortable with spin. If you want to talk about electrons to a 5th grader I’d be more inclined to say something like, “the electrons are all behaving the same way,” and just leave it at that. You can still talk about domains, you can still talk about temperature and thermal motion and how this destroys magnetism but I don’t think there’s anything to be gained by talking about spin. But maybe I’m wrong. I’m not used to teaching 5th graders.

    As for looking things up online I do think this is an important skill but I don’t think the student can get something meaningful out of looking up this question online. It seems to me that there are basically 3 situations in which you can look something up online: 1) there is a fact or value you need, 2) there’s a formula or algorithm that you learned before but now you don’t quite remember it and you need a refresher and 3) there’s some topic you don’t understand and want to know more about. Now 1) is pretty simple and I’m all for teachers getting students to look up facts. Teach students about moment of inertia, give them the moment of inertia for a solid sphere, have them solve some problems then on a homework problem have them look up the moment of inertia for a hollow sphere and use that to solve a problem. 2) is hit or miss depending on how well you remember the topic. Maybe the first week in pre-calc the teacher gives students some problems requiring them to use the quadratic formula or completing the square and students can get a refresher online. 3) is pretty darn difficult and I would say this question about magnetism falls into 3). Usually 3) only works if it’s an extended project that you spend time moving from one source to another and breaking a problem into pieces. If you look up a topic you don’t already have some understanding of online and you aren’t prepared to spend several days trying to understand what you’re reading then you’re going to end up writing down something you read verbatim because you don’t understand what you read. I very much hope that the teacher in this situation isn’t looking for 5th graders to bring in homework that says “the electron spins all line up when the metal becomes a magnet.”

    A quick example of the difficulty of using the internet for scenario 3): A friend who teaches a physical science class did a lab where students measured circumference and diameter of several discs to determine the value of Pi. One of the questions on the lab asked the students to calculate their uncertainty in C (circumference) and D (diameter) from their measurements. A student who was absent the day of the lab (and hence also missed the lesson about uncertainty) was making up the lab and the instructor told her if she wasn’t sure how to do the uncertainty calculation she could email him or she could look it up online because it isn’t that difficult. When the student turned in her lab for uncertainty she wrote delta_C*delta_D >= hbar/2. Clearly trying to learn uncertainty from Wikipedia when you don’t already have a starting idea of what to do can lead you astray.

  8. #8 meichenl
    January 11, 2010

    Hi Alex,

    To a fifth grader, I would say “all electrons are naturally little magnets all the time. Normally, the electrons’ magnets in an iron bar all point in different directions and cancel each other out. When you magnetize the iron bar, some of the electrons’ magnets line up to combine their strength. When you magnetize the iron bar even stronger, more of the electrons’ magnets line up. If you could line up the magnet of every single iron atom’s electrons, you’d have made the strongest magnet possible with that iron bar.”

    I don’t think a fifth grader would have a hard time understanding that if we drew some pictures and talked about it for a while. I wasn’t suggesting discussing spin with a fifth grader. I mentioned spin in response to Rhett’s claim that the electrons don’t change at all when iron is magnetized.

    This description has weaknesses, of course. It glosses over the point that most of the electrons are in lower orbitals and paired, and not contributing significantly to the magnetism of the iron bar. It also glosses over the idea of domains inside the iron. We could try to add those concepts in later. But I do think it makes sense to give a description in terms of electrons.

    As for internet research, yes, it’s difficult to learn about an unfamiliar topic, especially if you’re young. But the anecdote tells me that the student hadn’t learned much yet, and needs more practice, not that internet research is ineffective. Teachers who simply tell students to look something up probably aren’t helping much, but if the teacher has lists of good science resources for kids on the internet, and tries to get the students familiar with those resources to the point where the student can use them on his/her own, then that’s progress. I don’t know what some good sites for kids to learn science are because I don’t browse for that much, but I know that lots of universities and labs post public outreach sites, and there must be places to conglomerate and organize these resources.

  9. #9 jimmy
    January 11, 2010

    It’s not a bad question at all! It’s fascinating!

    But you answered with something she should just memorized. You changed electrons to “magnetic domains” and had her memorize that, with no real explanation or understanding. To use Feynman’s example, you just substituted “gravity” for “angels”, but didn’t do much else.

    Why not instead pull out some wire and a magnet and make an electro-magnet? Show her the relation between electrons moving in circles and magnetism – then talk about electron spin and magnetism. Easy, fun, and she’ll get the basic point.

    Oh – and for all you folks who are bagging on HS Science courses as being nothing but memorization: I’d like to see your sources. Cause when I look around, I see some of that, but not much. Certainly not in Physics, and certainly not in my school – and we’re just a lousy public school in a suburb of Boston.

  10. #10 Jim Thomerson
    January 11, 2010

    I once learned lots of things which I have forgotten. If I need to know them again, I know I can understand them anew because I knew at one time in the past. For example, I once learned elementary trigonometry. I have forgotten most of it, but if I need it, I will know that I need it, as well as where to go to refresh my memory. A person who has not studied trig would not have my advantage.

  11. #11 bsci
    January 11, 2010

    I think you’re missing a key part of the original question. Why iron and not aluminum? Your description explains why many substances can temporarily hold a magnetic “charge,” but not why iron retains that charge.

  12. #12 meichenl
    January 12, 2010

    Unfortunately, I don’t understand the fundamental reason aluminum and iron are different.

  13. #13 Rhett Allain
    January 12, 2010


    You get bonus points for invoking Zombie Feyman and you make a great point about memorizing the domain thing. However, there is an important point. A fifth grader could do some experiments to develop the idea of domains without having to just be told it.

    I use the Physics for Everyday Thinking curriculum for pre-service elementary education majors and they do just this. Now – electron spin, I don’t think there are any good ways to guide students with experiments to lead them to develop a model for this.

  14. #14 Dan
    January 13, 2010

    First you asked, “if you forgot it, did you really learn it in the first place?” I think the answer to that is yes. I can think of many things that I learned, like games, that I don’t remember how to do now.
    Second you said that she forgot her book. It is unclear that the teacher asked her to look it up online and she was just trying to find the answers from somewhere else. Most teachers that I know don’t have the students look up concepts online unless there is a specific site that they want the students to look up. Having kids just google stuff about science is just asking for crazy answers. If I asked my students to look up about global climate change, I will get answers from some Climate Audit or some other craptacular website.
    Knowing where to find the good, credible information is one of the things education is supposed to do along with making you go look it up and bring the information back in some synthesized form.

  15. #15 Leif Nabil
    January 16, 2010

    I remember seeing a video – perhaps Bill Nye or Beakman’s World – while I was your niece’s age that helped me construct a heuristic understanding of magnetism. The video explained that something was magnetic when all the electrons were lined up, pointing the same way.

    This wound up being a great foundation for building a more correct understanding that electrons spin and orbital motion induce magnetic fields that are summed.

    The heuristic understanding that your niece is comfortably capable of attaining is perhaps at the level of the video I mentioned above: Objects are magnetic when stuff inside them are *lined-up*. Which is a separate idea from positive things attracting attracting negative things.

  16. #16 Amiya
    January 19, 2010

    Excellent articles, finally, I may hope to hone my long rusted physics skills at this site. Rhett, exactly how do you solve the mass-energy problem from a magnet radiating magnetic energy? Is this energy transformation accountable by re/arranging of magnetic dipoles?

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