Re: electric permittivity and capacitors

On Oct 5, 11:36 am, boson boss <junker...@xxxxxxxxx> wrote:
I asked myself do I really understand why capacitors have greater
capacity with greater dielectrics.http://en.wikipedia.org/wiki/Permittivity
It appears to be simple: well polarized and arranged medium serves as
a transmission line from plate to plate. Also the field E is smaller
in the material with all the +-+-+-+-+- sums leading to zero.... so
this fits into energy going down inside capacitor with a great
dielectric.

Ok, let's see if you understand it. Here's one for the "brain fry"
series.

A capacitor consists of two square plates. Each plate is L x L. The
two plates are held a uniform distance apart, D. A dielectric material
is formed into a rectangular block L x L x D, and inserted between
the plates so that it just fills the volume between the plates.
The dielectric has a permitivity that is P times that of air. The
capacitor is charged to a voltage of V with the dielectric present.
Now consider moving the dieletric in a direction parallel to the
plates
but perpendicular to one of the edges. That is, you just slide it out
one side. What force will act on the dielectric as you slowly move
it all the way out of the capacitor? (Note: Ignore friction between
the plates and the dielectric.) What happens to the voltage across
the capacitor leads as the dieletric is removed?

Now if that one is too easy, consider this one:
A capacitor is formed of two parallel plates with a "spongy" dieletric
between them. Major Tom has decided he wants to use such things
as "electric bullets." He wants to use a small explosive charge to
make an abrupt geometry change in the capacitor so as to cause
the voltage across the leads to rise abruptly. What geometry
change should he attempt to produce to get a large spike in voltage?
Socks

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