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WHICH IS MORE "FUNDAMENTAL,"                  (c)1996 William J. Beaty
ELECTRIC CURRENT OR CHARGE?
http://amasci.com/emotor/fund.txt


Here's a perspective on Electricity which I've yet to encounter elsewhere.

The Ampere is far easier to measure than the Coulomb if the measurement
must be made with extreme precision.  Time (seconds) is also easy to
measure. Therefore, whenever physics standards are concerned, the Ampere 
and Second are measured, and the standard Coulomb is derived from them.

Unfortunately this concept has a very large impact on physics teaching and
educational materials, but it appears in an ugly, twisted form.  It
appears as an assertion that electric current is more "real" than charge.

It even appears as educators' unexamined assumption that electric current
is real, while electric charge is merely an abstract concept.  Not true!

The same error appears in K-12 school books, where it is claimed that
"quantity of electricity" is measured in Amperes, not in Coulombs.  The 
same books assert that "current electricity" is a fundamental type of
electrical substance, and they frequently state that "current" is the
substance which flows within wires.  Yet the "stuff" that flows in wires 
is called charge, not current.

The same problem appears in higher-level texts where students are taught
about Amperes, but they are often not given enough information to properly
visualize Amperes in terms of flowing Coulombs.  Sometimes students are
taught first about electric current and Amperes, and only later (if at
all) taught about Coulombs and about the electron sea of metals which does
the flowing. 

The idea that "Amperes are more real" also appears subtly all through non-
science electronics texts, where authors focus on current, on amperes, and
only ever mention the flowing "substance" in passing. 

The distorted concept appears in the widespread conviction that charge is
ghostly and unimportant, while electric current is real and substance-like. 

And it appears in the idea that electric charge only applies to "static
electricity", a phenomenon thought to be mostly useless (static cling, 
doorknob sparks) or even dangerous (lightning).  Conversely, Electric 
Current is supposed to apply to modern technology of nearly every kind.

I long have wondered where these various misconceptions arose, but
recently I suspect that they have a common origin.  I believe that our
method of standardizing physical units might be the cause.  The common
thread of these misconceptions is the fallacy that amperes are more
*fundamental* than coulombs, where the word "fundamental" is mistakenly
used in a popular sense, rather than with a specialized meaning pertaining
to standard physical units: "fundamental" units, versus "derived" units. 

In the everyday world, and using a popular meaning of "fundamental,"  we
would say that conserved quantities are more fundamental than rates.  For
example, Kilograms are more fundamental than Kg/seconds, volume is more
fundamental than flow rate, distance (meters) is more fundamental than
speed (meters/sec,) Joules of energy are more fundamental than Watts of
energy flow, etc.  For example, it would be ridiculous to introduce the
concept of speed to students who have little understanding of distance or
time.

But in electricity, many believe the opposite, and will fight fiercely for
their belief.  Some authors describe Amperes as fundamental units, and
point out that Coulombs are derived from Amperes.  They may introduce the
Ampere to students who have no grasp of the Coulomb.  They write as if
"electricity" is always measured in Amperes, while writhing that charge is
an abstract, hard-to-understand concept involving a strange unit called
the Ampere-second. 

I say, on the contrary.  Coulombs are fundamental, while Amperes are just
a convenient simplification of the concept called "Coulombs per second." 
Yes, the Coulomb unit is a Derived Standard, while the Ampere unit is a
Fundamental Standard.  Even so, electric charge is fundamental, and
electric current is just the flow rate of charge. 

This does seem to violate the statement that "Amperes are fundamental,
while Coulombs are derived."  But this statement is really saying that
"the physical standard for Amperes is directly measured, while the
standard for Coulombs is derived from Amperes and Seconds."  It's not
saying that Amperes are fundamental, it only discusses which unit is
easier to measure with precision.

When explaining electricity, I suggest that we avoid trying to teach about
alternate definitions of the word "fundamental", and avoid teaching about
Fundamental versus Derived units (at least in the lower grades).  We
should stick with the definition of "fundamental" which most students
already know.  I believe that the inexperienced learner will find
much more sense in the statement: 

  CHARGE IS MORE FUNDAMENTAL THAN CURRENT.  COULOMBS ARE A FUNDAMENTAL
  ENTITY, WHILE THE "AMPERE" IS SHORTHAND FOR "COULOMBS PER SECOND."

It is the charge which is "real," while the current is a rate; a flow; and 
abstract concept.

I also believe that students would be better served if the term "Ampere" 
was held back until later grades, and elementary electricity was taught
based on the concept of charge, and on amount of charge-per-second.  If
additional terms were introduced, they should be the terms "Coulomb" and
"Coulombs per second."  The term "Ampere" is shorthand, and should only be
introduced to students who have lots of experience thinking in terms of
"coulombs per second." 

Now, how does one convince a textbook publisher to take my ideas
seriously, when he or she can open most any physics book and find the
clear statement that "amperes are the fundamental unit"? 



(((((((((((((((((( ( (  (   (    (O)    )   )  ) ) )))))))))))))))))))
William J. Beaty                            SCIENCE HOBBYIST website
billbeskimo.com                            http://amasci.com
EE/programmer/sci-exhibits   science projects, tesla, weird science
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