Dielectric constant
In physics, the dielectric constant is a property of an insulator. It specifies the relative permittivity of a material. Where ε is the permittivity of the material in question, and ε0 is the permittivity of capacitors, and in other circumstances where a material might be expected to introduce capacitance into a circuit. If a material with a high dielectric constant is placed in an electric field, the magnitude of that field will be measurably reduced within the volume of the dielectric. This fact is commonly exploited to increase the rating of capacitors.
It is also crucial for the construction of dielectric waveguides.
- insert relation to refractive index
Example values for some materials
| Medium | εr | Refractive Index |
| Vacuum | 1.0000 | 1.0000 |
| Air | 1.0006 | 1.0003 |
| Paper (dry) | 2.0 | |
| Wood (dry) | 2-6 | |
| Rubber | 3.0 | |
| Dry soil | 3.9 | |
| Moist soil | 29 | |
| Water | 81 | 1.333 |
| Water (0 C) | 88.0 | |
| Water (100 C) | 55.3 | |
