Re: Let's start a new convention Teaching Magnetism

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

I wrote:

> I just meant that students might expect "Out" poles to display
> positive magnetic flux and "In" poles to display negative magnetic
> flux.

to which bc responded:

> Is that so bad?   +/- are correctly? often used to indicate directions.
> Is the problem they will ascribe to + or - more than just a direction?

and cb (!) responded:

> I'm still trying to see the confusion with G's law. An Out 'pole'
> within the gaussean surface WOULD make a mathematically positive
> contribution to the total flux. Some or all of the Out poles
> contribution could be counterascted by any In poles that also are
> within the surface in question.
>
> If your objection is that G's Law can be confused by the concept of
> Poles, then I agree. I am suggesting that IF poles remain in the
> students science vocabulary, then it would be better for them to be
> considered as being Out and In poles (or Ludwik's choice of Head an
> Tail also has that nice warm intuitive feel that we all seek so
> diligently  ;-)

(I'm not sure that I understand either of these comments.  It may be
that we are simply talking past each other.  And in responding I may
risk having someone think that I think I'm making an important point.
I don't, nevertheless ...)

My point had only to do with the fact that the things we generally
*call* "magnetic poles" are not *really* magnetic poles.

Of course, if there are *real* magnetic poles, the terms "In" and
"Out" would be perfectly consistent with Gauss' law as they also
would if they were applied to electric charges.  The terms could even
assist in the use of Gauss' Law.  We'd have the pleasant property
that nonzero net numbers of field lines really do go "into" In poles
and come "out of" Out poles.  (As Roger pointed out, however, we
would lose the geographical connection and a nice opportunity to
force students to simply think it all through.)

But if we apply the terms "In" and "Out" to the "not real magnetic
poles" (perhaps we should call them "pseudopoles") that *appear* to
reside in the vicinity of the ends of a bar magnet or a solenoid, we
will find that just as many lines of magnetic induction go into as
come out of each type of pseudopole.

So my point was simply that the terms N and S may better avoid the
implication that lines end on In poles and begin on Out poles, an
implication that seems somewhat inherent in the terms In and Out.

John
--
John Mallinckrodt        mailto:ajm@csupomona.edu
Cal Poly Pomona          http://www.csupomona.edu/~ajm