Re: felt dismissed

[William Beaty <billb@ESKIMO.COM>]

On Sat, 8 Jun 2002, Hugh Haskell wrote:

> > Until you get to the undergrad level,  nobody ever tells you that in some
> > materials the outer electrons have left their atoms.   Nobody ever tells
> > you that a "conductor" is not transparent to charge flow, but instead a
> > "conductor" simply contains mobile charges.

I should qualify this.  In my own experience, in courses about circuits,
nobody ever told me that copper is full of charge.  Also, I was taught
that insulators block the flow of "electricity."  Yet in chem class I
learned about "metallic bonds" and the sea of electrons, but I suppose
that this information went into a separate mental pigeonhole.


> Good point, Bill. I know that when talking about it, I do take care
> to always talk about the "free electrons"  in a conductor, but I'm
> not sure that I have been as explicit as perhaps I should have been
> in emphasizing that point. I guess that I just never thought about it
> as a student misconception. It would appear that I was wrong. I will
> be more careful about that in the future.


I like to make trouble by calling the word "electricity" into question...
like so:

   Metals are full of electricity.   When you make a circuit out of
   copper wire and then connect it to a battery, the electricity of
   the metal wires is forced to flow.   It flows through the battery
   and back out again.

   When a flashlight is operating, the charges flow like so:  they
   start out in the light bulb's filament.  Then they flow through the
   filament and out to the wire leading to the battery.  The battery
   pumps them through itself.  Then they flow out through the other
   battery terminal, and wind up back in the filament again.

This statement includes several things:  it uses the word "electricity" as
physicists once used it.  It contradicts the "charge is energy" concept
and the "batteries supply charge" concept which are taught in early
grades.  It also avoids talking about "current" as if "current" was a
substance (don't say "flow of current.")  It also emphasizes the proper
definition of a "conductor" as being a substance which contains mobile
charge, rather than the "conductors are like hollow pipes" fallacy.

Separate topic:  people on sci.electronics newsgroups think that air and
vacuum are conductors.  After all, a vacuum cannot block the flow of
charges, and look at vacuum tubes and CRTs.  And sparks leap through air.
(But poke your ohmmeter leads into the air, or into a vacuum, and doesn't
this demonstrate that air and vacuum are insulators?  One would think that
this would end the argument!)



I finally had a brief opportunity to try out the above "electricity"
explanation on kids in 4th grade.  I got the strong impression that many
understood it, and their teacher even performed a brief verbal post-test
with the class, and most did parrot back the right answers.  So who knows,
maybe it works.



(((((((((((((((((( ( (  (   (    (O)    )   )  ) ) )))))))))))))))))))
William J. Beaty                            SCIENCE HOBBYIST website
billb@eskimo.com                            http://amasci.com
EE/programmer/sci-exhibits   science projects, tesla, weird science
Seattle, WA  206-789-0775    sciclub-list freenrg-L vortex-L webhead-L