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Re: Order of E&M topics (was B and electric charge)

I like Robert Cohen's discussion of the sequence for introducing EM
concepts. I must protest however that I neither invented nor advocate doing
circuits first - although it may have its place. The CASTLE curriculum by
Melvin Steinberg, now being distributed by PASCO, has been around since at
least 1990.

The electrical force - and electrostatics - can be introduced as part of
mechanics. David Hestenes of ASU Modeling Method fame, in one of his
lectures. presented the vision of distinguishing and characterizing the
various kinds and manifestations of force as a part - the final part - of
the study of Newton's laws. The standard Modeling curriculum does not at
this point realize this vision.

Camp and Clement, in "Preconceptions in Mechanics", present a research-based
and well-worked-out introduction to various manifestations of force:
tension, compression including the "normal force", static and kinetic
friction, and finally the gravitational force. Out of this they develop an
effective treatment of Newton's third law, the failure to fully grasp which
produces the "70% barrier" in most modeling physics classes - the inability
of most modeling instructors to achieve higher than a 70% class average on
the Force Concept Inventory (FCI). (Still way beyond what traditional
instruction can achieve.)

Camp and Clement fall short however in not having a fully developed
investigation of Newton's first and second laws and in structuring their
curriculum so that it is still controlled from the front of the class. When
I used their text straight my classes got restless and their comprehension
and retention were limited. The synthesis would be to weave their
investigations and "bridging techniques" and the "modeling method"
curriculum into a seamless, model-building, peer-instruction curriculum
which includes careful investigation of the manifestations of contact force,
buoyant force, the electrical force and electrostatics (introducing a
primitive concept of current but without introducing the field, which is
conceptually much more difficult), the force between two wires, and then the
gravitational force - perhaps using a video of the Cavendish experiment with
data generated but *no interpretation provided*. (Does anyone know of such a
video? I was unable to locate one.)

Doing the electrical force first - and uncovering the inverse square law
there - should help a lot in winning the students' grasp of the inverse
square gravitational attraction. Finally then, starting with a reexamination
of gravity as it occurs in a classroom, the concept of a field can be
developed.

So we sneak a big hunk of the rest of physics into mechanics. In the process
we deflect the criticism of spending too much time on mechanics - which we
really needs to do if students are going to become Newtonian thinkers. I
expect we would smash the "70% barrier" on the FCI. And we would realize
David Hestenes' vision of a mechanics course which truly forms a foundation
for all of physics.

The next order of topics could be circuits a la CASTLE (or the Modeling Task
Force rewrite of CASTLE to put it in a peer instruction project-based
framework), then linking circuits to charges a la Sherwood and Chabay.

Thermodynamics is so essential to student understanding of energy and
chemical phenomena that it should be included here. I would urge anyone to
study the awesome article "Introductory Thermal Concept Evaluation" by Yeo
and Zadnik in the November "Physics Teacher" for some insight into the
central importance and challenge of tackling this material. Certainly if
physics is to be a preparation for chemistry as in the "physics first"
project this is a fundamental responsibility.

That would definitely fill a school year, and would be a year well spent.

Chris Horton




* * * * * * * * * * * * *

Christopher A. Horton, Ph.D.
4158 RR#3 (Hwy. 204)
Amherst, NS B4H 3Y1
CANADA
ChrisAHorton2@hotmail.com
(902) 447-2109

* * * * * * * * * * * * *

"Many discoveries are reserved for ages still to come, when memory of us
will have been effaced. Our universe is a sorry little affair unless it has
in it something for every age to investigate ... Nature does not reveal her
mysteries once and for all."
- Seneca, "Natural Questions", first century, quoted by Carl Sagan in
"Cosmos", p.xi.

* * * * * * * * * * *


----- Original Message -----
From: Robert Cohen <Robert.Cohen@PO-BOX.ESU.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, January 04, 2002 11:49 AM
Subject: Order of E&M topics (was B and electric charge)


I am very interested in this discussion since I use an order that
is similar to what Ludwik Kowalski describes. Still, I think the
order we use depends on the audience. I teach algebra-based physics
and I wouldn't follow the same sequence if it was the calculus-based
sequence.

FWIW, some of the things I intend to do that are somewhat unconventional
are
as follows:

1. I first cover electric force, without introducing the concept of a
field.
2. When discussing electric potential, I also discuss binding energies
(without
E=mc2) and fusion/fission.
3. I cover AC circuits right after DC circuits, without first discussing
magnetism. I find I can describe what an inductor does without having to
explain why it does what it does.
4. I introduce magnetism via the force between two wires.
5. I introduce fields qualitatively in terms of defining a direction,
which
I apply to gravitational, electric and magnetic fields.
6. I then quantify fields using g=F_g/m; E=F_e/q; B=F_m/IL; I first use
this
to identify the fields associated with point objects (and wires) then I
use
this to quantify the force on an object given an externally applied field.
7. I then investigate induction in order to investigate how an inductor
works.

--------------------------------------------
Robert Cohen rcohen@po-box.esu.edu
570-422-3428 http://www.esu.edu/~bbq
Department of Physics
East Stroudsburg University
East Stroudsburg, PA 18301
--------------------------------------------

-----Original Message-----
From: Ludwik Kowalski [mailto:kowalskiL@MAIL.MONTCLAIR.EDU]
Sent: Friday, January 04, 2002 8:41 AM
To: PHYS-L@lists.nau.edu
Subject: Re: B and electric charge


Thanks for good questions, Jack. I have no objection to what
you wrote (se the end of this message). But I would not say a
"standard charge"; any arbitrary charge, or a distribution of
charges, can be used to verify that two point-like charges are
equal. I will be away for a week. Perhaps the debate on the
sequence of electric concepts (in the first physics course) will
continue when the semester starts.

What I would like to discuss is the definition of B. Why do
we define it in terms of the EFFECT of the magnetic field
and not in terms of what CAUSES it? Instead of introducing
B via the Lorentz law (directly or indirectly) we can introduce
it via the Bio Savart law. Which way is pedagogically more
desirable and why? I have no opinion so far.

I also think that Chris Horton's idea of "circuits before
electrostatics" (see below) is worth debating. I think that a
minimum of electrostatics is necessary before circuits but
not everything we cover under this part of the course. In
other words, start with a minimum, introduce circuits and
return to both fields at the end.
Ludwik Kowalski