"electric current" is not electron flow

[William Beaty <billb@ESKIMO.COM>]

On Sat, 6 Oct 2001, John Clement wrote:

> 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.

Electrostatic charge transfer is not well understood, and I've seen
frequent mention that, for some types of materials, "frictional charging"
is probably caused by the transfer of ions both neg and pos types, not of
bare electrons.

In K-6 textbooks we often find the misconception that electric current is
always and forever a flow of negative charges.  Since this error appears
in the textbooks, I assume that many educators believe this misconception
as well, and must be teaching it to their students.  I don't know if this
is still true in grades 7-12, but I've met many technical people who still
believe that electric current is defined as a flow of electrons, and that
postive charges cannot flow at all.


> 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.

Good point.  The situation could be like the "solar system" atom model in
introductory chemistry.  Atoms don't look like little solar systems, but
as long as the mental model doesn't create future learning barriers, it
can be a useful tool.

But looking at myself and my mistaken belief that "electric current is
electron flow", I'm forced to say that serious barriers are created.

Because I believed that current in circuits was ALWAYS a flow of
electrons, I was never able to form a coherent and intuitive picture of
how electric circuits worked.  Instead I did what most electrical
engineers do: I gave up any hope of ever being able to fully visualize the
physics, and instead started relying on the equations more and more.  This
let me become a circuit designer. But my knowledge of the physics remained
shallow until (among other things) I was forced to face the idea that
electric current is NOT a flow of electrons as I'd always been taught.


> 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.

This is a major issue.  I found a good analogy:

  Rather than trying to teach the "sound wave" concept, we should tell
  our students that loudspeakers and vocal chords emit sound particles,
  and these little bullets fly out in all directions at 720MPH until they
  strike a distant eardrum and are heard as sound.

Obviously it's possible to create misconceptions during an attempt to come
up with something that younger the students can grasp.

Now that I'm thinking about it, perhaps the problem is not with students'
"concrete" thinking level.  If we say that electric current means
"electron flow", in concrete terms that's just plain wrong.  Changing the
sign of the Conventional Current does not magically make it "concrete."
To paint a concrete picture, we must say that electric current IS
DEFINITELY NOT a flow of electrons.  Instead it's a flow of many different
things:  opposite pairs of ions flowing in salt water (including within
your body), or electrons and positive ions flowing through plasmas and
liquid metals, or free protons flowing frozen water.  Ice is a proton
conductor.  Oh yeah, and free electrons flowing through solid metals.

If "concrete" is required, we shouldn't try to hide it behind a negative
version of conventional current!


> 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.

Or perhaps they should talk about CHARGE FLOW, with just a nod at
"electric current."  In other words, teach about all the situations where
positive charges flow.  In the end this will demonstrate why the "electric
current" concept is so useful:  it greatly simplifies things by
emphasizing the flow rate while hiding all the stuff about charge velocity
and direction.



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