Symbol: e
Unit: farad meter-1
(F m-1)
The permittivity of a substance is a characteristic which describes how it affects any electric field set up in it. A high permittivity tends to reduce any electric field present. We can increase the capacitance of a capacitor by increasing the permittivity of the dielectric material.
The permittivity of free space (or a vacuum), e0, has a value of 8.9 × 10-12 F m-1.
The permittivity of a material is usually given relative to that of free space, it is known as relative permittivity, er. Permittivity is then calculated
by multiplying e0 by this figure.
Material |
Relative permittivity, er |
| Vacuum | 1 (by definition) |
| Air | 1.0005 |
| Polythene | 2.35 |
| Perspex | 3.3 |
| Mica | 7 |
| Water | 80 |
| Barium Titanate | 1200 |
We can increase the capacitance of a capacitor by increasing the permittivity of the dielectric material.