Re: Appropriate for Gen Phys? was: comprehending electric/magnetic interactions

[John Clement <clement@HAL-PC.ORG>]

It certainly is a reasonable explanation, however the MOP series gives
students a "formal model".  After exploration, the formal model is
presented, and students are asked to reason using it.  Notice that this
is a classic learning cycle.  They are then asked to distinguish between
charges and "nanomagnets".  The domain structure is only touched on.
The primary idea that students must work with is that macroscopic
magnets consist of "nanomagnets" which are aligned for greatest
strength.  They have already seen this effect in labs, and have seen
that N and S poles are never separated.

One of the things that is being demanded is that any statement they come
up with must be consistent with all of the facts.  For example they see
that bar magnets produce a stronger magnet by putting N to N & S to S.
They also see that disk magnets are stronger when N & S are together on
top of each other.  They have to give up simple N to N or N to S and
instead think in terms of microscopic magnets or nanonmagnets lining up.

They also have to realize that magnetic forces are NOT electrical forces
and that different models apply.  With the beginning students this is
very important.  A connection is made between them, but at this level
they have to learn to distinguish between them.  Learning to reason with
formal models is actually at the higher level of formal reasoning
according to the Piagetian classification.

At this point, many HS physics courses talk about electrical forces, but
never really do anything with magnetic forces.  The misconception that
magnets work by electrical forces is never properly addressed as a
result.  Students still harbor the belief that magnets interact with any
metal, and they never make the connection between compass needles, the
earth, and magnets in the laboratory.  Incidentally magnets are often
mentioned in history, but students usually do not make any reasonable
connections there either.

By the end of the combined electric, magnetic, gravitational unit many
students are beginning to make distinctions, but sadly some are not.
The "wrong" explanation is only "wrong" at the end, and is a perfectly
good idea part way through.  I would also prefer to call a "wrong"
explanation an inconsistent explanation with the model.  This actually
mirrors the way science proceeds.  At any given stage "wrong"
explanations are just explanations that are not consistent with current
model or paradigm.

John M. Clement
Houston, TX

>         Exactly!  What experiment demonstrates that the "dropping
> the magnetic particles" explanation is wrong?  The entire philosopy
that
> most of us want to promote is "learning from experiment".  So there is
a
> level at which "particle dropping" is as good a hypothesis as any.
>         In my experience it adds fun and interest to the classroom to
> tentatively adopt primitive explanatios - the only proviso is that the
> explanations must eventually be tested.
>
>
>
>
> > Brian Whatcott    Altus OK