The dielectric constant ε(relative) environment is a physical quantity that characterizes the properties of the dielectric (insulating) environment. It is associated with the effect of dielectrics polarization under the influence of an electric field. The dielectric pronitsaemosti shows how many times less than the force of interaction of electric charges in any environment than in a vacuum.
To determine the permittivity of a substance er, compare the capacity of the condenser, taken as a test, with the specified dielectric (Cx) and capacitance of the same capacitor, but in a vacuum (Co): Ɛr = Cx/Co
Dielectric permittivity of most gases, including air, under normal conditions approaches unity (due to their low density). A large part of the solid dielectric has a relative permittivity, which is in the range of 2 to 8. In a static field, dielectric constant of water is of sufficiently high value of approximately 80.
Substances with molecules that possess a significant electric dipole have a large value of the dielectric constant.For example, the permittivity of ferroelectrics is tens or hundreds of thousands.
Dielectric permittivity is one of the most important parameters when creating capacitors. The use of materials which have high dielectric constant can significantly reduce the geometric dimensions of the capacitors.
Capacity electric capacitors is determined by the formula: C= Ɛr*Ɛo*S/d

er — dielectric constant of the insulator between the plates,

EO is the electric constant,

S — the surface area of the capacitor plates,

d — the gap between the plates.

Dielectric permittivity is taken into account when creating printed circuit boards.