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Re: Earth's Magnetic Field



I didn't even know there was any confusion on this. The way I've
always taught it, and every book I have says:

The north geographic pole is a south magnetic pole. Therefore, when
examining a magnet, the pole orienting itself toward geographic north
is the north magnetic pole of that magnet.


Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817



-----Original Message-----
From: Larry Smith [SMTP:Larry.Smith@SNOW.EDU]
Sent: Monday, May 10, 1999 4:37 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Earth's Magnetic Field

Seems like this topic has come up before, but I just received a
shipment of
new equipment for our lab and read the following in the instructions
for
the Electro-Technic Magnetizer:

-------begin quote------
The convention for marking polarity for compass needles is to mark the
pole
seeking the Earth's north magnetic pole with a "N". That way sailors
are
not confused when directed to steer a course. The convention for
marking
bar magnets is such that a compass needle will point in the direction
of
the lines of flux as though they were traveling from the "N" pole to
the
"S" pole. This places the "N" at the end of the bar that if suspended
as a
compass needle will point north. Relative to the Earth's magnet field,
a
Nort seeking pole has to be the south pole of the bar. Opposite poles
attract. Even so, the convention is to makr it "N".

The Model 28000 Magnetizer is marked with a "N" on the right side and a
"S"
on the left. When operated, the magnet produced causes a compass
needle's
north seeking pole to point to the end placed into the "N" cavity. A
magnet produced by the magnetizer if suspended by a string woudl point
the
end marked "N" to the south which is exactly opposite to the
convention.

The logic for doing it this way is that most customers are unaware of
the
convention, and in the beginning one of our distributors complained
when a
magnet thus produced caused a compass needle's "N" pole to be attracted
to
the "S" pole of the magnet. We did some testing and discovered that
most
inexpensive magnets are made with the polarity reversed. So
Electro-Technic bowed to the popular perception even thought it is
counter
to the convention. IN all the years and thousands of magnetizers sold,
the
number of complaints about polarity have been very few.

For some, this may pose a problem. If you have inadvertently
magnetized
your magnet backwards, and have been inconvenienced by this problem, we
apologize. If you want to reverse it, simply magnetize it correctly by
placing the magnet pole marked "N" into the "S" cavity of the
magnetizer
and the magnet produced will be configured in accordance with the
convention.
---------end quote-------

If I'm even understanding this clearly, it seems to be backward to the
way
H&R and Serway have it. True, a convention is just a convention, and
we
could have done it the other way; so I don't care which way we decide
to do
it, as long as we can all agree together. What is the vote on this
list
for the convention?

Thanks,
Larry Smith