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Re: Let's start a new convention Teaching Magnetism



Hi,

Why not go back in history and explain that the
compass predates almost all of physics and
geophysics. The North pole of a compass and more
generally a magnet is a NORTH SEEKING pole.

I think it is a big mistake to make a major
change in vocabulary to make an already simple
idea easier for students to "get." School is
about teaching thinking, and if the students
cannot understand the this simple idea, the
schools have totally failed. The geographical
North pole being a magnetic South pole is only two
logical steps: 1. the north pole of a magnet is
attracted to the south pole of other magnets; 2.
since the north pole of a magnet is attracted to
the north geographical pole of the Earth, the
North Geographical pole of the Earth must be a
magnetic South pole. The world is filled to the
brim with concepts, and ideas that are orders of
magnitude more complex and subtle than this.

Yes the students have to overcome a misconception
and maybe think for a whole minute, but it will be
good for them, trust me.

Thanks
Roger Haar
U of AZ

*******************************************
Chuck Britton wrote:

Let's start a new convention. Many have noted that the geographic
word 'north' gets fatally confused with the physics word 'north'.
Some say that we shouldn't teach about magnetic 'poles' since they
seem to not exist. but we still need a convention to specify field
directions.

I propose (seriously - for once) that we retain the pole concept (for
historical, pedagogical reasons) but refer to the poles as the 'In'
pole and the 'Out' pole. Then the direction of the field is just the
direction of whatever it is that is pointing in or out.

Seems to me that this would work for ferro-magnets, solenoids, even
for the electron dipole moment.

Anybody see any problems with this convention? It seems much more
useful that choosing OTHER opposite words suggested like up/down,
light/dark etc.

At 1:33 AM -0400 7/8/03, Michael Edmiston wrote:

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

--
.-. .-. .-. .-. .-. .-. .-. .-. .-. .-
\ / \ / \ N / \ C / \ S / \ S / \ M / \ / \ /
`-' `-' `-' `-' `-' `-' `-' `-' `-'
Chuck Britton Education is what is left when
britton@ncssm.edu you have forgotten everything
North Carolina School of Science & Math you learned in school.
(919) 416-2762 Albert Einstein, 1936