

The permittivity of an insulating, or dielectric, material is commonly symbolized by the Greek letter epsilon, ε; the permittivity of a vacuum, or free space, is symbolized ε0; and their ratio ε/ε0, called the dielectric constant (q.v.), is symbolized by the Greek letter kappa, κ.

In the rationalized metre-kilogram-second (mks) and SI systems, the magnitude of the permittivity of a vacuum ε0 is 8.854 × 10−12. Its units and those of permittivity ε are square coulombs per newton square metre. In the mks system, permittivity ε and the dimensionless dielectric constant κ are formally distinct and related by the permittivity of free space ε0; ε = κε0. In the centimetre-gram-second (cgs) system, the value of the permittivity of free space ε0 is chosen arbitrarily to be 1. Thus, the permittivity ε and the dielectric constant κ in the cgs system are identical; both of them are dimensionless numbers.

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Space in which there is no matter or in which the pressure is so low that any particles in the space do not affect any processes being carried on there. It is a condition well below normal atmospheric pressure and is measured in units of pressure (the pascal). A vacuum can be created by removing...
property of an electrical insulating material (a dielectric) equal to the ratio of the capacitance of a capacitor filled with the given material to the capacitance of an identical capacitor in a vacuum without the dielectric material. The insertion of a dielectric between the plates of, say, a...
where ε0 is called the permittivity of free space and has the value of 8.854 × 10−12 coulomb squared per newton-square metre. In addition, ε0 is related to the constant k in Coulomb’s law by
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