Re: cathode rays - historical question

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

> On 04/06/2003 12:48 PM, Mark Sylvester wrote:
> > The answer affects how I teach the background to the discovery of
the
> > electron. There is already the wave/particle discussion about light.
If
> > there is good reason to mention differences here then I want to do
so.
> In
> > fact, I have for years talked about a particle vs continuum debate,
and
> am
> > wondering if I've been wrong all this time.
>
> The pedagogical question is central.
>
> IMHO the so-called wave/particle "debate" gets too much
> emphasis in many classrooms.  Why bring it up at all?
>
> 1) In general, the history of physics is a poor guide to
> the teaching of physics.  Kuhn had something to say
> about this.  Typically the "historical" approach leads
> to a distortion of the history and sometimes a distortion
> of the physics as well.

Actually there is some very good evidence that a historical approach can
improve student understanding of concepts.  An optics course in
Australia was reported in AJP where they used a historical approach and
had students consider how the ideas evolved historically.  They used a
conceptual pre and posttest which was also used in a conventional
course.  The result was that the historical achieved twice the gain of
the conventional course.

> The history of science is an _advanced_ topic, open
> to those who already understand physics and already
> understand the methods of historical inquiry.
>
> Students have a limited time budget.  Historically,
> the facts were discovered in convoluted and difficult
> ways.  The best evidence nowadays for the nature of
> electrons doesn't come from Thomson's experiments.
> Why not give the students the best evidence and
> leave it at that?
>
> 2) It has long been known (deBroglie 1924) that there
> is no real distinction between the physics of waves
> and the physics of particles.  So why foist on the
> students a false and useless distinction?

It may be that the students need to go through the same changes in
thinking that happened historically.  There may be an optimal sequence
for teaching QM that needs the wave / particle distinction.  It may be
that this distinction is built into the way that we see the world, and
that confronting it may be absolutely necessary to gaining understanding
of QM.  The fact that students have to go through certain stages to gain
higher level thinking skill has been demonstrated by the experiments of
Piaget. In a similar fashion it is quite probable that there are
important stages that can not be skipped on the way to understanding QM.

This particular research is now going on as we speak.  I have not paid
as much attention to the QM PER papers, but I believe there are some
from McDermott's group that may shed some light on this debate.  No
amount of logical debate can actually settle this question as it is an
experimental question.  "Does confronting the particle/wave distinction
play an important role in improving student understanding of QM?"

> If you're going to do history, do it right.  Even
> then, remember it is usually not a good guide to
> teaching the facts and concepts of science as presently
> understood.  And it's not even a good guide to how
> science should be done;  past scientists have made
> plenty of mistakes.

The history presented to students does not have to be complete in order
to produce the Piagetian surprise necessary to trigger accommodation.  I
will agree that the history has been treated badly, as evidenced by the
number of books that present "The Scientific Method".  At present the
history has been taken out of many of the books and students often
receive a bland pablum devoid of historical context.

Another point that should be made is that there is a large body of
evidence that points to the ineffectiveness of the current practice of
providing proven neat connections to the students.  Most students do not
get the meaning from the proofs presented by well meaning instructors.
The students do not understand the meanings that are intended, and
instead construct very different concepts.  This difficulty is
exacerbated by the fact that instructors follow a sequence that seems
logical to them, but is actually very ineffective.  At present, most
curricula are laid out by one or another logical schemes which do not
work well.

The student time budget is currently not spent well as most research
shows that conventional courses achieve only <=25% gain in
understanding.  Including history is one of several approaches that may
improve this figure.  Currently most teachers will say that they can not
do the types of activities that improve understanding because they have
too much to cover.  This particular excuse is producing many students
with extreme math and science phobia.  Math teachers use this excuse to
justify not using manipulatives, and science teachers use it to justify
not using inquiry.  As a result over half of my HS seniors could not
tell me that the distance around a merry-go-round was PI x the distance
across.  I took the time to have them measure it!!!!!

Perhaps there are some members of this list who are engaged in research
on QM learning who could shed some light on this question?

John M. Clement
Houston, TX