I think that we are stuck with the name "displacement current". I
try to emphasize to my students that this was a bad choice of words, since
nothing is being "displaced" nor is it a "current" in the same sense as
the other currents they deal with in electrical problems. I then
emphasize that epsilon-0 times d(phi)/dt is numerically equal to the
current in the wire, but that it really is d(phi)/dt that is the
interesting physical quantity. I find that this is a great opportunity to
point out that there are two different sources for magnetic fields
(currents, and time-varying electric fields).
I also point out that the magnetic field generated by the
"displacement current" between the plates of the capacitor is different in
an important way from the magnetic fields that they have dealt with
before. It is easy to show that it has a 1/r spatial dependence, so it is
a radiation field. Previously, they have seen that a localized,
time-varying electric field produces an electric field with a 1/r spatial
dependence. This paves the way for the discussion of e.m. waves.
Mark
Dr. Mark H. Shapiro
Physics Department
California State University, Fullerton
P.O. Box 6866
Fullerton, California 92834-6866