Re: coulombs

["Richard W. Tarara" <rtarara@saintmarys.edu>]

My $.02 on this.  The electron charge is what is really fundamental,
however the standard unit (for intro work) for charge IS the coulomb.  Most
intro texts hit electric force and electric field before doing current
electricity, hence the coulomb is introduced before the ampere.  However,
all the problems and examples end up using micro-coulombs or nano-coulombs
to keep the forces and fields from being unreasonably large.  The student
is also faced with the fact that the electron charge is 1.6x10^-19 C and
there are 6.8x10^18 electron charges in a coulomb.  This leads students(or
should lead them) to the obvious question--Why is the unit for charge so
damn large?  The answer, of course, is in Williams first statement
below--the ampere was measured before the coulomb and is still an easier
measure to accomplish.  

So while charge should be considered more fundamental than current, the
common unit of charge was derived from current measurements.  I assume
(does anyone know for sure?) that at some point, the Coulomb and Ampere
were adjusted (at least in principle--since we're talking 18 or more
decimal places) to be an exact integral multiple of the electron charge.

----------
> From: William Beaty <billb@eskimo.com>

> The ampere is far easier to measure with precision than is the coulomb.
> The second is easy to measure.  Therefor, the ampere and second are
> measured, and the coulomb is derived.
>
>
> I say, on the contrary.  Coulmbs are "fundamental," while amperes are
just
> a convenient simplification of the concept "coulombs per sec."  And,
while
> this violates the concept "fundamental vs derived" it is more correct
than
> the reverse, and I believe that it makes much more sense to the
> inexperienced learner.
>
> Now, how does one convince a textbook publisher to take this idea
> seriously, when he/she can open a physics book and find statements saying
> "amperes are the fundamental unit."