Re: Current Flow (shouldn't it be "charge flow?")

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

The point of view of teaching the subject should actually be different from
the view that a professional physicist has.  While it is convenient to
specify charge as a continuous property, this point of view produces
confusion for the beginning student.  Anton Lawson in a remarkable series of
papers in Jour. of Res. in Sci. Teach. (JRST) has shown that concepts which
involve "invisible" things are much more difficult for students to
understand.  He has shown that these concepts are generally more accessible
to students who have thinking skills at a level that he calls the
"Theoretical" level.  This level of thinking would be above the "formal
operational".  Since less than 20% of students who graduate from HS can be
classified as "formal operational" the level of understanding of charge or
current can be fairly difficult for the majority of students.

Students do seem to readily accept the idea of protons and electrons, though
again understanding may be low because they are "unobservable".  Defining
charge in terms of properties of these elementary particles should help them
make more sense of the physics because it gives them a more concrete picture
of what it means.  Rather than charge flow, electron flow would be used.
This also ties in with the one way flow model of electrostatic charge.
While this does not address such topics as ion flow in solutions or holes in
semiconductors, it provides a more understandable model.  Once this model is
well understood, then conventional current and other models can be
introduced.

The low understanding is readily probed by some fairly simple questions.
One question that I frequently use is to ask students what fraction of the
electrons are removed from an object when it is charged positively.  (a)100%
(b) 50% (c) 5% (d) 1% (e)an extremely low fraction.  You might be surprised
by your student's answers.

John M. Clement
Houston, TX

> I have to repeat what I said the last time around on this (Leigh then
> chastized: Of course - that goes without saying!):
>
> Our physics is a model, not reality itself - it is couched in OUR way of
> thinking - which is to distinguish between SUBSTANCES and their
> PROPERTIES.  These concepts and distinctions are about our working model
> of reality - we are not asserting that they are externally so. We are
> reifying within our model - not in the external world.
>
> Bob Sciamanda (W3NLV)
> Physics, Edinboro Univ of PA (em)
> trebor@velocity.net
> http://www.velocity.net/~trebor
> ----- Original Message -----
> From: "Hugh Haskell" <hhaskell@MINDSPRING.COM>
> To: <PHYS-L@lists.nau.edu>
> Sent: Saturday, April 20, 2002 3:44 PM
> Subject: Re: Current Flow (shouldn't it be "charge flow?")
>
>
> At 11:02 -0600 4/20/02, Jim Green wrote:
> >  >
> >  >I, for one, don't believe so.  Electrons have the property of mass and
> > > charge.  Electrons flow through the wire.
> > >
> > > Brian McInnes
> >
> > Right you are, Brian, and praise to you for pointing this out -- but we
> > physicists -- well, some of us -- insist on reifying properties. It is a
> > disappointing habit -- which competent physics teachers should persist in
> > trying to obliterate.
>
> Just what is an electron if not the sum of its properties? And what
> is reality? Reification gets decried, but just what is reification if
> we don't even know what reality is? I don't see how we can talk about
> electrons or anything else except in terms of its properties, be they
> permanent or temporary.
>
> Hugh
> --
>
> Hugh Haskell
> <mailto://haskell@ncssm.edu>
> <mailto://hhaskell@mindspring.com>
>
> (919) 467-7610
>
> Let's face it. People use a Mac because they want to, Windows because they
> have to..
> ******************************************************