# Re: Glass dilectric constant

```On Sun, 29 Nov 1998 22:27:05 -0700 in the Tesla List
<kc1-at-ime-dot-net> wrote:

>I've seen plenty of different dilectric constant values for glass...
>anyone know if the value of, say, wine bottle glass?  Closer to five or
ten?

There's a good reason for all those different values of dielectric
constant for glass,
glass is a very variable product! There is only one way to know the
dielectric constant of any given batch of glass and that is to measure
it. You can do this quite simply by making a capacitor out of the glass
in question and carefully measure its: thickness and the effective area
of the plates then plug these values into the classic capacitor equation
and solve for dielectric constant. I have done this in the past for wine
bottles and got values from 3 up to 7. The only glass I ever measured
that approached a dielectric constant of 10 was vicor and that stuff is
VERY EXPENSIVE, besides you will quickly learn that the dielectric
constant isn't nearly as important as the dielectric strength. If you
take the equation for a capacitor and play with it you find that for a
unit change in dielectric constant you get little change in the end
capacitance, BUT if you can make the plates a tinny bit closer you get a
BIG increase in the end capacitance. This is why almost all of us have
settled down with polyethylene film, it's dilectric constant isn't very
high at all in fact it's around 3 BUT it's dielectric strength approaches
1KV per mil that beats glass and and almost everything else hands down!
You should also consider power factor because that is a measure of the
energy wasted as heat in the capacitor, glass has a relatively high power
factor but polyethylene has a very low power factor so glass capacitors
are going to waste more energy and get hotter also putting them further
at risk of shattering! BTW each and every glass capacitor I ever made
eventually ended with an explosive breakdown, with glass flying all over
the room. Even enclosing them in wooden enclosures didn't prevent them
from starting a fire upon breakdown within the box.

will answer them!        Most people are very uncomfortable conversing
with unknown and especially secretive       people.
Sincerely

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