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Re: EPSILON_ZERO, OK ?



Let us invent our own unit of Q and call it S (after Satan). The
immediate consequence of this is that the unit of k must be
N*m^2/S^2. What is the numeric value of k? It depends on
how large is one S. If S is large then k is small, and vice versa.

HA ha ha :^).

Please verify that the above definition of Coulomb implies that
k=8.99*10^9 N*m^2/C^2. It turns out that 4*Pi can be eliminated
from some derived formulas if k is written 1/(4*Pi*epsilon_zero),
where epsilon_zero is 8.8542*10^-12 C^2/(N*m^2). The name
given to epsilon_zero, "permittivity of free space", can not be
appreciated in this introductory physics course.
Ludwik Kowalski


Ahhh, but you can relate epsilon_zero to something: mu_zero. You will
have to explain mu_zero later in your same course. After that you will
have to discuss the relationship between mu_zero and epsilon_zero and
the speed of light c as was (perhaps I am wrong here) discovered by
Maxwell while playing with the units of epsilon_zero and mu_zero
and trying to make a constant with units of velocity. So you have
a complete and coherent story line for epsilon_zero across three
chapters. This puts you ahead of most intro physics texts, which
have problems maintaining notation (let alone a conceptual story line)
across chapters.

I'd encourage you to do a little hand-waving on Gauss' law, which ties
epsilon_zero to k and starts the chain. And definitely keep the
Satan system; I'll have to try that myself :^).

Dan, who has no real intention of going to Law School although he
is often encouraged to develop precision in language in a lawyerly
fashion.

Dan MacIsaac, Assistant Professor of Physics and Astronomy, Northern AZ Univ
danmac@nau.edu http://purcell.phy.nau.edu PHYS-L list owner