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Re: electric charge

The choice of fundamental dimensions is arbitrary, though, of course, some
choices are more useful than others. A dated, but still very good, summary
of dimension and unit systems is found in "Nuclear Engineering Handbook" by
Harold Etherington.

For mechanics, the CGS, MKS, and SI systems choose length (L), mass (M),
and time (T) as fundamental dimensions, and force is a derived
dimension. Such MLT systems are so-called "absolute systems." But, in the
engineering system, length, time, and force (pound-force) are fundamental
dimensions, and mass (slug) is a derived dimension.

For electrical systems, a fourth fundamental dimension is chosen. In the
SI system, current is a fundamental dimension.

In the old absolute electrostatic (aes) system, permittivity is the
fundamental dimension (the unit of permittivity is the permittivity of the
vacuum). The statcoulomb is the charge which exerts a force of one dyne on
an equal charge one centimeter away. Statcoulomb, statampere, statvolt,
etc. are derived units in the aes system.

In the old absolute electromagnetic (aem) system, permeability is the
fundamental dimension (the unit of permeability is the permeability of the
vacuum). The abampere is the current which exerts a force of one dyne per
centimeter of conductor on an equal parallel current one centimeter
away. The abampere, abcoulomb, abvolt, etc. are derived units in the aem
system.

For thermodynamic systems, the fundamental dimension is termperature or
heat (or energy). Etherington refers to systems of five fundamental
dimensions which describe mechanics, thermodynamics, and electromagnetism
as "universal" or "comprehensive" systems.

Glenn A. Carlson
St. Charles Community College

Date: Fri, 21 Dec 2001 00:25:02 -0500
From: Joe Heafner <heafnerj@VNET.NET>
Subject: electric charge

Another hopefully simple question. Is electric charge a
fundamental dimension or is it not? I've seen some texts
treat it as a dimension and some that do not. Which is it?