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

[William Beaty <billb@ESKIMO.COM>]

On Sun, 21 Apr 2002, Tim O'Donnell wrote:

> Would it be better for me to define a 1 ampere current to
> be to flow of 6.24 X 10^18 electrons and not even
> mention coulombs.  Students at least think they have an
> understanding of electrons.

I eventually traced my own conceptual troubles with batteries to a
misconception:  the misconception that electric current is a flow of
electrons.  In reality electric current is a flow of charged particles.  A
proton beam inside a particle accelerator is an electric current, just as
the drifting electrons in a copper wire is an electric current.  When you
touch your fingers to 120V terminals and receive a painful shock, no
electrons flowed through your body, even though there might have been many
tens of milliamperes worth of current in your finger.

Here's another misconception I had about batteries: one plate is an
electron source, and that the other plate is an electron sink (and no
charges flow in the electrolyte between the plates.)  When I finally
figured out that a battery is a "charge pump", and finally saw that the
source/sink model is incorrect, my understanding of batteries took a great
leap forward.

Here's an explanation of a flashlight which is almost totally correct, but
which violates the stereotypical textbook explanation.  (Educate by
provocation?)  :)

   An electric current is a flow of charged particles.  In a simple
   flashlight the charges start out inside the filament of the
   light bulb.  When the switch is closed, the charges are pulled out of
   the filament, they flow along one conductor and into one end of the
   battery, then they are pumped through the battery and flow out through
   the other terminal.  They flow along the second conductor, and
   eventually end up back inside the filament of the light bulb.


The above paragraph might cause the reader to think that the filament of
the light bulb is the source of the charged particles.  This was my
intention.  The filament IS the source!  (Well, the filament AND the
conductors AND the battery plates AND electrolyte supplies the movable
charged particles.)   In my experience, most people end up thinking that
the battery supplies the electrons which flow through the circuit.  Not
only is this a wrong idea, it acts as a misconception which blocks further
learning.


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William J. Beaty                            SCIENCE HOBBYIST website
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