Re: Narges instead of charges?

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

The problem of having negative carriers actually goes deeper than just the
direction of current flow.  Students have the misconception that
electrostatic charge transfer usually occurs by various means other than
transfer of electrons.  The single carrier model is very difficult for most
of them to grasp.  Having a positive carrier might make this easier,  but it
probably would mask the real problems that students have.

In high school over 80% of graduates do not test at the formal thinking
level, so the difficulty with negative charge carriers is extremely large.
(in my class only 15% of the incoming students test at the formal level) A
coherent picture of "electricity" which involves the flow of electrons, and
the transfer of electrons in electrostatics helps students grasp the
concepts.  As a result, I talk about electron flow rather than conventional
current.  This practice used to be common in some texts, could be revived
for the beginning student.  Once they have a firm grasp of the concepts, and
have moved to a higher level of thinking, the use of conventional current
could then be introduced.

While this may seem to be roundabout, it does not involve changing existing
terminology.  Instruction involves talking about electron flow rather than
using the word current.  This has the advantage of providing a concrete
meaning.  Since the vast majority of my HS students do not go on to take
another physics course, using nonconventional terminology is not really a
problem.  I do point out that the word current is used as if there were a
flow of positive charges in the opposite direction, but I avoid actually
using the word in most situations.  The students who do go on to another
physics course are usually the students with  higher level thinking, and who
can more easily grasp the idea of conventional current.

Since the word positive and negative are just arbitrary labels for the types
of charge, having the negative ones flow just makes this fact more obvious.
We could call them male and female, or black and white or ...  The
pedagogical problems are not readily solved by a simple switch of positive
to negative, nor is it solved by just the change that I propose.  The
problem is made easier by the use of electron flow, as part of a coherent
picture of what happens in materials.  In addition various labs such as the
batteries and bulbs labs are vital to help students visualize the correct
picture.

I think that all of the elementary texts that might be used with lower level
thinkers should talk about electron flow with maybe a nod at conventional
current.  The upper level texts could then use conventional current while
still pointing out the physical visualization of what is going on.  More
abstract concepts such as fields would remain unchanged.

John M. Clement
Houston, TX

> On Fri, 5 Oct 2001, Ludwik Kowalski wrote:
>
> > Suppose the original convention was different. In that case
> > the conventional direction of electric current would coincide
> > with the direction along which electrons drift in wires under
> > the influence of DOP. Pedagogically this would be more
> > convenient than the situation in which the two directions
> > do not coincide.
>
> But then the large difference between "charge flow" and "electric current"
> would be almost completely obscured!