Dielectric Constant:

Dielectrics are things that do not conduct electricity well, if at all. Dry air is a great example of a dielectric. A wall is another. Materials have different dielectic constants at room temperature. For example, air is about 1, paper is 3, rubber is 7. The dielectric constant is the ratio of the electrical conductivity of a dielectric material to free space. Tools like an electronic stud sensor uses the property of dielectric constants to measure the relative density of a wall and identify when that density changes, as when the sensor passes over a wood stud.

The dielectric constant is the relative permittivity of a dielectric material. 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 used to increase the capacitance of a particular capacitor design. The layers beneath etched conductors in printed circuit boards (PCBs) also act as dielectrics.

Dielectrics are used in RF transmission lines. In a coaxial cable, polyethylene can be used between the center conductor and outside shield. It can also be placed inside waveguides to form filters. Optical fibers are examples of dielectric waveguides. They consist of dielectric materials that are purposely doped with impurities so as to control the precise value of er within the cross-section. This controls the refractive index of the material and therefore also the optical modes of transmission. However, in these cases it is technically the relative permittivity that matters, as they are not operated in the electrostatic limit.

The relative static permittivity of a solvent is a relative measure of its polarity. For example, water (very polar) has a dielectric constant of 80.10 at 20⁰C while n-hexane (very non-polar) has a dielectric constant of 1.89 at 20⁰C. This information is of great value when designing separation, sample preparation and chromatography techniques in analytical chemistry.