What is the dielectric constant of the medium

Back in school at physics lessons, the teacher, talking about electrical phenomena, explained what the dielectric constant of the medium is. In the future, if the main profession is not connected with electrical engineering, the topic was safely forgotten. In this paper, we will recall what is behind this definition.

Usually to explain the term "dielectric permittivity of the medium" it is customary to consider an example with a capacitor whose plates are flat. Imagine the simplest condenser in a vacuum. Let us determine the value of the electric charge :

Qv = (U * S * Ev) / d,

Where d is the distance between the plates, U is the voltage, S is the area of the plate, and Ev is the dielectric. constant. The latter is the reference value, it is the dielectric constant of the medium without air (vacuum) and is equal to 8.85 * 10 to a power of -12 Farad per meter.

But in the capacitors of the separating plate, the medium can be not only a vacuum, but also any other dielectric material. Obviously, in this case the dielectric constant of the medium differs from "Ev", and therefore the charge varies. If the capacitor is connected to the EMF source, then the value of the charge on the plates becomes Qz. The dielectric constant of the material is the ratio of the charge of the plates of the connected capacitor Qz to the charge in the case of the vacuum Qv, i.e.,

E = Qz / Qv.

Obviously, there is no dimension. A powered capacitor consumes additional power from the source.

In fact, this is the relative permittivity of the medium. It shows how many times the intensity of interaction of charges separated by a dielectric decreases, compared with plates in a vacuum. It can also be said that this is one of the characteristics of the material.

If, however, when the charge on the plates accumulates, the energy supply stops, another phenomenon takes place. The voltage value decreases and, as a consequence, the electric field strength decreases . Why?

Any material consists of atoms with electrons rotating around the nucleus. When an electric field appears, the charge carriers are dispersed in each molecule according to the polarity of the external action - there is a so-called polarization forming a dipole. This is its electronic form. The material itself can consist of both polar and nonpolar molecules. In the first case, the molecule is oriented according to the field (voltage), and since the dipoles self-orient, the relative permittivity is rather high. The value of their permeability often exceeds 100 units. In the second case (nonpolar molecules), although the dipole field is formed due to the action of the dipole field, part of the energy is spent on maintaining their spatial configuration, therefore permeability is insignificant and rarely exceeds 5 units. It is worth noting that the gaseous substance always has a low permeability index due to the small number of molecules per unit volume, regardless of their natural structure.

For most common dielectric materials, permeability data are given in the corresponding tables, so when performing calculations, there is no difficulty in determining the desired value. It is interesting that air has a permeability of 1 unit. This explains why in the capacitors various additional dielectric layers are used - ceramics, mica, paraffin, etc. All these materials, having a higher permeability, increase the value of the charge accumulated on the plates. In other words, the capacitance can be regulated not only by the arrangement of the plates, but also by the material separating them. Champions among substances with high permeability are ceramics (about 80) and purified from impurities water (not less than 81).