The relative permittivity of a substance is a measure of how it affects an electric field. The higher the relative permittivity the lower the electric field through that substance. It is often the case that the relative permittivity for a substance is given instead of the absolute permittivity, but the relative permittivity can be used to calculate the absolute permittivity quite easily. The relative permittivity is sometimes known as the dialectric constant.
The absolute permittivity of a substance is denoted by ε and it is equal to the absolute permittivity of a vacuum, ε0, multiplied by the relative permittivity of that substance, εr. This gives us: ε=ε0×εr. The value of ε0 is 8.85×10-12 Fm-1. The table below shows some materials, their relative permittivity, and their permittivity.
| Material | εr | ε |
|---|---|---|
| Glass | 8 | 7.08×10-11 |
| Vacuum | 1 | 8.85×10-12 |
| Water | 80 | 7.08×10-10 |
Fischer-Cripps. A.C., The Electronics Companion. Institute of Physics, 2005.
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