Why is as important as What. When If I know a collection of facts but do not
understand why they are so, I have no principles that I can apply in order to
apprehend other facts. So when struggling to understand something I may
appear to be arguing, as in stating that the other person is wrong. While I
have been known to do that some times, usually what I'm doing is trying to
get my mind around the facts.
That I never took college level physics may explain my difficulties, then
again maybe not since I don't know to what extent the issue of 'where a
charge is stored in a capacitor, might be answered by college level physics,
at least as much of it as an EE might take. As a technician I have often had
to just accept some premise, not having the knowledge to question them or to
verify them for that matter. And being pragmatic I see no problem with that
as long is it doesn't interfere with what I may be trying to do. For
example, who care which convention is used, current of electron flow as long
as we can follow the function of a circuit. Likewise knowing whether a
capacitors charge is stored, the plates or the dielectric won't help me
understand why the capacitor seems to allow current to flow right through it.
In fact I can operate as current does flow though the capacitor and when
working with them in actual circuits we assume a capacitor to be an AC short
circuit, albeit a frequency sensitive one.
All of this leads me to quote from Nigel Cook, DC-AC Second Edition, 1993.
In chapter 11, under the summary on capacitance he actually states that the
'charges on the plates produce an electric field...' Sound like he's saying
that the charge is stored on the plates. The last sentence in the paragraph
states...
'The energy in a capacitor is actually stored in the electric field within
the dielectric.' Sounds like it's stored in the dielectric. Now some
interpretation which I would be allowed if I were a student reading this
book, but which could be mistaken. Nothing new, I've been wrong before and I
plan to be wrong again before I go to that great capacitor in the sky to be
fully charged for eternity. :-)
I think both views may be wrong. The energy is stored in the electrostatic
field, not on the plates, not in the dielectric. That certainly would explain
why vacuum capacitors can work. It also agrees with my notion that a
conductor can't really store a charge. Oh, and this also agrees with the
idea that energy is stored in the magnetic field in an inductor, which always
seemed strange to me.
Am I right, is one of the other view right? I really don't give a poop. But I
have an explanation that will satisfy me until someone comes up with a better
one. And I feel that I understand capacitors better now. Maybe I'll take one
out to dinner some time.
Jim
