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

[Robert Cohen <Robert.Cohen@PO-BOX.ESU.EDU>]

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