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The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulator measures the ability of the insulator to store electric energy in an electrical field.
Another common term encountered for both absolute and relative permittivity is the dielectric constant which has been deprecated in physics and engineering [2] as well as in chemistry. [ 3 ] By definition, a perfect vacuum has a relative permittivity of exactly 1 whereas at standard temperature and pressure , air has a relative permittivity of ...
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field.When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor, because they have no loosely bound, or free, electrons that may drift through the material, but instead they ...
A dielectric gas, or insulating gas, is a dielectric material in gaseous state. Its main purpose is to prevent or rapidly quench electric discharges . Dielectric gases are used as electrical insulators in high voltage applications, e.g. transformers , circuit breakers (namely sulfur hexafluoride circuit breakers ), switchgear (namely high ...
The refractive index n of the gas can then be expressed in terms of the molar refractivity A as: n ≈ 1 + 3 A p R T {\displaystyle n\approx {\sqrt {1+{\frac {3Ap}{RT}}}}} where p is the pressure of the gas, R is the universal gas constant , and T is the (absolute) temperature, which together determine the number density N .
Dielectric films tend to exhibit greater dielectric strength than thicker samples of the same material. For instance, the dielectric strength of silicon dioxide films of thickness around 1 μm is about 0.5 GV/m. [3] However very thin layers (below, say, 100 nm) become partially conductive because of electron tunneling.
Various methods may be employed to create voids or pores in a silicon dioxide dielectric. [3] Voids can have a relative dielectric constant of nearly 1, thus the dielectric constant of the porous material may be reduced by increasing the porosity of the film. Relative dielectric constants lower than 2.0 have been reported.
[13] [16] Hence, the term "dielectric constant of vacuum" for the electric constant ε 0 is considered obsolete by most modern authors, although occasional examples of continuing usage can be found. As for notation, the constant can be denoted by either ε 0 or ϵ 0, using either of the common glyphs for the letter epsilon.