In October, I am teaching a week of lessons to fourth-graders on electromagnets and (to a lesser degree) electricity. I have a pretty good understanding of the “thats” of magnets: I know that magnets have north and south poles, that you make an electromagnet by coiling wire around a core and running electricity through it, that electromagnets are used to power electric motors, and so forth.
What I lack is a solid grounding of the “whys” of magnets: why do non-electromagnets attract iron, and why do they have poles, and why is this effect replicated by wrapping wire around a core and running electricity through it?
The best page I’ve found that explains it is this one, and it doesn’t go into the detail that I need. There’s always this page, but I’m afraid it goes into so much depth that I quickly get out of mine.
Is Ambrose Bierce accurate, or can someone give me an explanation of magnets that will allow me to satisfy the “whys” of a bunch of fourth-graders?
Probably not. The best explanation of magnetic “why” is quantum mechanical but nobody explains “why” quantum mechanics. It just is. Magnetic materials can be though of as consisting a bunch of little magnets all pointing in random directions which is the state of smallest net energy stored in the magnetic field. If the material is subjected to a sufficiently strong external field, or aligned with, say, the earth’s field and struck sharply, the little magnets will tend to line up in one direction and leave the material magnetized.
As to electro magenets. If you have a wire carrying current there is a magnetic field surrounding the wire. You could get some dry cells, a resistor and some wire, and a manetic compass. Hook up a circuit and show that when there is a current in the wire the compas is affected. Try it at home first so you get all your ducks in line.
The magnetic field around the wire has a definite direction and when you wrap it around a piece of iron the fields all are in the same direction around the turns of the coil of wire thus formed and this magnetizes the iron. Actually there is a magnetic field around just a plain coil in the air too. However the presence of the iron core greatly increases the magetic field.
Answer.com has some pretty easy to understand info.
A good demonstration of magnetic fields uses iron filings. Carefully sprinkle the filings on and round the magnet and you should see something like this.
That sounds awfully like Mr. Bierce’s answer :). It may be that the kids won’t ask me the question, but if they do, I may just need to say, “It requires a Ph.D. in physics to understand the answer to that,” and leave it there.
The experiments y’all are describing sound pretty similar to what I already have planned. I’m not sure if I can get enough compasses so that everyone can try it out, but there will definitely be enough dry cells, iron cores, and wires that lab groups can make their own magnet.
I don’t know if it exists, but if Isaac Asimov ever wrote an article about magnetism, that’s what I would want to use to teach children about the subject. I seem to recall reading an essay by him on the subject, but Googling didn’t turn anything up.
As far as explaining it to children, my suggestion would be to focus on how it works and what use it is to us. For the ones who have to know the why of it, just look them in the eye and tell them that they have the opportunity to become famous by discovering that.
I’d put a few intermediate levels in between “because it’s a magnet” and “you’d need a PhD to understand it”. You could tell them, for instance, that all magnets consist of electric charges travelling around and around. This is fairly obvious in an electromagnet, of course, but it also applies to a permanent magnet. It’s just that there, the charges that are going around are the electrons of the individual atoms, going around the nucleus.
If you’ve seen electric forces (a plastic comb attracting bits of paper, for instance), you might also mention to them that electric and magnetic fields are really just two different aspects of the same thing, as shown by Maxwell over a century ago, and that it was the fact that electricity and magnetism are really the same thing that led Einstein to the realization that matter and energy are also two aspects of the same thing, and that space and time are also the same as each other.
For those unfamiliar with Ambrose Bierce’s The Devil’s Dictionary, he defined a magnet as something acted upon by magnetism. And in the elementary, macro physics world we haven’t come a whole lot further than that.
Yeah, that’ll clear things up. Tell 'em that matter and energy are the same thing.
Anyway, you could mention that there are four “fundamental forces” and (electro)magnetism is just one of them. The “whys” of magnetic attraction are no more, or less, confusing than “why” an apple falls to the ground. Magnetic attraction just works across a distance, like gravitational attraction.
As a way of demonstrating just how much stronger electromagnetism is than gravity, you can tell the kids that you can use a magnet to pick up another piece of metal. Essentially, that magnet is exerting a force strong enough to counteract the gravitational force that the entire earth is exerting on the metal.
Many fourth graders will have heard that Einstein found an equivalence between matter and energy. Very, very few of them will understand it, but they’ve probably seen the equation a time or two. And drawing connections like this just might fascinate a few of them enough that they’ll learn the physics so they can understand it.
I’ve come up with what to say to people when explaining what electricity is, and magnets are pretty closely related. I explain that electron flow is not what electricity “is.” Electicity “is” the electric field, and that electric field causes electrons to move. So now the question becomes “what is the electric field?” And the answer to that is: no one has an intuitive understanding of that.
We can do calculations that will exactly predict what is going to happen, and it does happen that way every time, to an astounding degree of accuracy. In that sense, and that sense only, we understand electricity. But if you really want to get to a gut-level understanding, you can’t.
I think this kind of explanation, adapted to include magnetism, and not taking very much time, would be interesting to fourth graders.
I guess you could go one step further and say that electric charges exert forces on each other and electric fields are the forces. Then all that remains is What are electric charges? Well, they are whatever it is that exert those forces. At bottom it gets to be like trying to define the very first word in a dictionary.
Sure you are. You haven’t even made plans for building the solar system sized accelerator you’ll need to get up to GUT energies yet, have you? To say nothing of the infrastructure you’ll need to service it out beyond minor planet 134340. Slackers!