### Re: electrical conductivity, permittivity, dielectric constant?

Date: Tue May 1 02:28:32 2001
Posted By: Karl Kolbus, Staff, Data processing, Mequon Consulting Corp.
Area of science: Physics
ID: 988009177.Ph
Message:
```
Hi Manik!
First off, dielectric is not the opposite of electric. A dielectric is a
material which does not conduct an electric current because the lines of
force of an electrostatic field will pass through it, making it the seat
of the strain.

Permittivity is the same as dielectric constant (also sometimes
called 'specific inductive capacity'), and is a measure of the ratio of
electric displacement to electric field intensity. Permittivity( Greek
symbol sigma) determines the potential capacitance of 2 parallel plates
separated by a dielectric, and is affected by temperature, pressure, and
the frequency of the applied voltage, and is subject to the inverse square
law, more commonly called Coulomb's Law. Permittivity calculations are in
relation to the sigma of a vacuum (8.85 x 10 to the minus 12th) being
assigned a value of 1.00.

The dielectric constants of some common materials are: air 1.0004947,
water (at 25 deg. C.) 78.54, water (at -22 deg. C.(ice)) 40, wood (oak)
2.4 to 6.8, Chloroform 4.806, Zinc Carbonate 100.  As you can see, some
liquids have a higher value than some solids and vice-versa. Most gasses
are slightly above 1. The higher the value, the less conductance. Given
the same area of the plates, and the same distance between them, a
material with a higher dielectric constant (permittivity) will conduct
less, allowing a greater buildup of opposite charges on the plates,
resulting in a greater capacitance.

I've included a link to a simple capacitance calculator. Play with the
numbers and materials. I think everything will become clear, if it isn't
now.

I hope this puts things in perspective for you.

By the way, you're probably thinking "What's this nut thinking about -
using water as a dielectric? Water conducts electricity".
........ not PURE water!! It's all that other junk in water that makes it
conduct.

Karl

KarlKolbus@ameritech.net

http://www.woodsbas.
demon.co.uk/calcs/calcs.htm

```

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