Electric permittivity and dielectric constant
- table or chart of the electric permittivity or dielectric constant of a
material. This figure is important because it determines the capacitance between
two plates. One of the factors
The permittivity is another term for the dielectric constant
or a material. It is that property of a dielectric material that determines how
much electrostatic energy can be stored per unit of volume when unit voltage is
applied.
| Substance |
Relative
Permittivity |
| Ebonite |
2.7 - 2.9 |
| Glass |
5 - 10 |
| Marble |
8.3 |
| Mica |
5.6 - 8.0 |
| Paraffin wax |
2 - 2.4 |
| Porcelain |
4.5 - 6.7 |
| Rubber |
2.0 - 2.3 |
| Calcium titanate |
150 |
| Strontium titanate |
200 |
| |
|
| Air 0C |
1.000594 |
| Air 20C |
1.000528 |
| Carbon monoxide 25C |
1.000634 |
| Carbon dioxide 25C |
1.000904 |
| Hydrogen 0C |
1.000265 |
| Helium 25C |
1.000067 |
| Nitrogen 25C |
1.000538 |
| Sulphur dioxide 22C |
1.00818 |
The values given above are what may be termed the "static"
values of permittivity. They are true for steady state or low frequencies. It is
found that the permittivity of a material usually decreases with increasing
frequency. It also falls with increasing temperature. These factors are normally
taken into account when designing a capacitor for electronics applications. Some
materials have a more stable level of permittivity and hence they are used in
the higher tolerance capacitors. However this often has to be balanced against
other factors. Some materials have very high levels of permittivity, and hence
they enable capacitors to be made much smaller. This factor may be particularly
useful when the size of the capacitor is particularly important.
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