Permittivity

From HvWiki

Physical property that describes a material's ability to resist developing an electric field. Symbol $ε$ .

The permittivity of free space, or permittivity of a vacuum, is:

$\epsilon_0 \equiv \frac{1}{c^2\mu_0} \approx 8.8542 \times 10^{-12} \cdot \mbox{C}^2 \cdot \mbox{N}^{-1} \cdot \mbox{m}^{-2}$

This is very close to the permittivity of air.

The permittivity of a material is generally written as a dielectric constant. This compares it to the permittivity of the vacuum (or "free space") so a dielectric constant of 20 would mean a permittivity of $20\times\epsilon_0$ . For paper this constant is between about 1.5 and 3, for glass it's about 4 to 14 and rubber about 2 to 4.