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Re: Teaching Magnetism



1. A lot of confusion can be avoided by using more words on the label.
The directions that came with my magnetizer said "put the end of the
magnet that you want to become north into the hole marked N." But I
knew most people would not read the directions and/or the directions
would get lost. So I put my own labels on the device that said, "put
north pole here" and "put south pole here."

2. Likewise, I have a large alnico C-magnet from a (really old really
large) computer disk drive unit. I use it as a "keeper" for my
soft-iron bar magnets. Originally I properly labeled the alnico magnet
poles as N and S and I put the bar magnet N to the alnico S. However, I
soon found that students and other profs were using the bar magnets and
then returning them to the keeper "backwards." Either they didn't
understand magnets, or they were confused as to whether the N label
meant "this is the north pole so put the bar south pole here," or
whether it meant "this is where you put the north pole of the bar
magnet." So I relabeled the alnico magnet to say "put N-pole of bar
magnet here."

3. Although almost all sources I am aware of say the north geographic
pole of the earth is a south magnetic pole, I have observed (even in
print) that some people think earth's geographic north pole is a north
magnetic pole, and therefore they think the compass end that points to
geographic north is the south pole of the compass. If any of these
"backwards people" are responsible for putting the labels on
magnetizers, they will label the magnetizers incorrectly, all the while
thinking they are correct.

BTW, I poll my physics class each year to see how they think the
earth's poles are defined. That's a good exercise, and it doesn't take
them long to realize there needs to be a convention as to whether
geographic north is magnetic north, making the geographic-north-seeking
pole of a compass a south magnetic pole, or vice-versa. If they have
not yet read the textbook before I poll them (typical) the class usually
splits about 50-50 as to which way they think it should be. After I
tell them the convention physicists have adopted is that earth's
geographic north pole is a magnetic south pole, the students that
guessed backwards still think their way is better and that physicists
made the wrong choice. This is somewhat similar to how students react
who think the direction of electric current should be defined by
electrons rather than the direction positive charges would go.

Also, after having this discussion, whenever a student says north pole
or south pole I always query them as to whether they mean geographic or
magnetic. I want them to develop the habit, when speaking of earth, of
including the word geographic or magnetic as a required adjective in
front of pole. They catch on pretty quickly, although they continue to
be annoyed I bug them about it. When they say, "You know what I mean,"
I say, "No I don't."

Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Chair of Sciences
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu