Re: SI and electric charge

[Chris Horton <ChrisAHorton2@HOTMAIL.COM>]

IMHO the Coulomb is the most logical fundamental unit, once the technology
of counting electrons is fully developed.  The fundamental conserved
quantity being measured is the charge on a certain number of electrons,
protons, etc.  The use of current as the fundamental quantity is a
historical artifact.

Which one is introduced first is another matter.  If we start with circuits,
the Ampere has to come first.  If we start with electrostatics, the Coulomb
comes first.  IMO starting with electrostatics and developing the concept of
current from there - perhaps following the path laid out by Chabay and
Sherwood (Sp?) - is conceptually sounder, but circuits do get the students'
attention and interest.

Student gains on some concept mastery instrument should of course be the
final arbiter.  Has anyone tried to measure and compare the effectiveness of
these two sequences?

Chris Horton

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Christopher A. Horton, Ph.D.
4158 RR#3 (Hwy. 204)
Amherst, NS B4H 3Y1
CANADA
ChrisAHorton2@hotmail.com
(902) 447-2109

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"Many discoveries are reserved for ages still to come, when memory of us
will have been effaced.  Our universe is a sorry little affair unless it has
in it something for every age to investigate ... Nature does not reveal her
mysteries once and for all."
- Seneca, "Natural Questions", first century, quoted by Carl Sagan in
"Cosmos", p.xi.

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----- Original Message -----
From: Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, January 03, 2002 10:08 AM
Subject: SI and electric charge


> More I think about SI more convinced I am that a change in the
> way of presenting this system to students will be beneficial. The
> old status quo tolerated four systems of units, practical and three
> absolute (CGSE, CGSM and Gaussian). This was not good and
> SI was an improvement. But there are many ways of introducing
> SI units in teaching. Conceptually any electric unit can be the
> first (in a sequence of definitions); starting with coulomb does
> not change anything in SI, provided the number of electrons in
> coulomb does not change. I am not trying to invent another
> system of units. One system for all is highly desirable and it
> should be used in all introductory physics courses.
>
> SI resulted from merging the idea of rationalization (1/4*PI in
> Coulomb's law), the idea of using four basic units instead
> of three, and the idea of making electromagnetic units absolute
> (rather than standard-based). Non of the above changes when
> C is introduced before A, when epsilon_o and mu_o are
> combined into one experimentally measurable (?) constant
> called speed of light, or when 4*PI is dissolved in the
> numerical definition of the first unit, such as coulomb.
>
> So why should coulomb, and not ohm or farad, be the
> first unit in a teaching sequence? Because the first electrical
> concept of that sequence is electric charge. If another (?)
> pedagogical sequence the first unit would change without
> changing the SI. What is wrong with this? How many of
> us think that defining C before A is harmless? How many
> think it is worth promoting? No, I am not asking for a vote;
> these questions are rhetorical. But please share your opinion.
> Ludwik Kowalski
>
> > Let me add that the main reason for making A fundamental,
> > rather than C, was practical, not conceptual. Forces between
> > macroscopic currents can be measured more accurately than
> > forces between macroscopic charges. Those who promoted
> > SI ignored pedagogical considerations. That is what I think.