It seems to me that it makes a difference as to whether you are going to be
teaching Gauss's Law or not. When I teach electricity at a level that
Gauss's Law will not be mentioned, I am inclined to use k. However, if
Gauss's Law lurks around the corner, I wish my textbook would introduce
epsilon-sub-zero right from the start. Students don't understand why we
switch from k (in Coulomb's Law) to epsilon-zero (in Gauss's Law). In some
ways the switch is good because it gives me the opportunity to talk about
the spherical symmetry around point charges, and how the 4-pi is going to
naturally crop up, etc. Even so, when I switch from k to epsilon, some
students feel like the chessboard got upset and they have to start over
again.
By the way... I have an additional complaint about this. Why do we use
epsilon-zero instead of epsilon? Or to ask it the other way, why do we use
k and not k-zero. It seems to me that Coulomb's Law and Gauss's Law should
be written just with k and/or epsilon. The vacuum case is a special case.
If Gauss's Law were written with epsilon it would be correct for any medium.
If written with epsilon-zero it is only correct for vacuum. Granted, air is
almost the same as vacuum, but at least half of my students are chemists and
they are going to be doing work in solutions, etc., where the dielectric
constant is very different from one... for example, about 80 for water. So
the electric field around point charges in water is 80 times smaller than
would be predicted by Gauss's law using epsilon-zero. If GL were written
with epsilon it would make it more clear that you have to use the correct
epsilon for the medium at hand.
Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817