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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 ...
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 .
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 ...
[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.
A table of some typical values can be found under dielectric constant. Water has a relatively high dielectric constant value of 78.7 at 298K (25 °C), so in aqueous solutions at ambient temperatures 1:1 electrolytes such as NaCl do not form ion pairs to an appreciable extent except when the solution is very concentrated.
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.
The strong polarity of water is indicated by its high dielectric constant of 88 (at 0 °C). [5] Solvents with a dielectric constant of less than 15 are generally considered to be nonpolar. [6] The dielectric constant measures the solvent's tendency to partly cancel the field strength of the electric field of a charged particle immersed