Relative Permittivity
Key Stage 5
Meaning
Relative Permittivity is the ratio of the Permittivity of a medium compared to the Permittivity of Free Space.
About Relative Permittivity
- Relative permittivity of a medium is denoted with the Greek letter epsilon followed by a subscript of r (\(\varepsilon_r\)).
- Relative permittivity has no units.
Equation
- When an electrostatic field propagates through a medium which is not the vacuum the permittivity of that medium is given by the product of its relative permittivity and the permittivity of free space.
\(\varepsilon=\varepsilon_r\varepsilon_0\)
Therefore
\(\varepsilon_r=\dfrac{\varepsilon}{\varepsilon_0}\)
Example Media
| Medium | Relative Permittivity |
| Air | 1.00054 |
| Glass | 4.7 |
| Water (at 0°C) | 88 |
| Steam (at 100°C) | 55 |