The Dielectric constant reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Dielectric constant

In physics, the dielectric constant is a property of an insulator. It specifies the relative permittivity of a material. Where &epsilon is the permittivity of the material in question, and &epsilon₀ is the permittivity of free space, the dielectric constant &epsilon_r is defined as the ratio:

In vacuum (free space), the permittivity &epsilon is just &epsilon₀, so the dielectric constant is unity:

The dielectric constant is an essential piece of information when designing 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

External links

• Full Dielectric Constant Table

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