Back at school, in physics classes, the teacher, talking about electrical phenomena, explained what the dielectric constant of a medium is. In the future, if the main profession is not related to electrical engineering, the topic was safely forgotten. In this paper, we recall what lies behind this definition.
Usually, to explain the term "dielectric constant of a medium" it is customary to consider an example with a capacitor whose plates are flat. Imagine the simplest capacitor in a vacuum. We 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, Ev is the dielectric. constant. The latter is a reference value, it is the dielectric constant of a medium without air (vacuum) and is 8.85 * 10 to the degree of -12 Farad per meter.
But not only vacuum, but any other dielectric material can act as a medium in the capacitors of the separating plate. Obviously, in this case, the dielectric constant of the medium differs from "Ev", and therefore the charge changes. If the capacitor is connected to the emf source, then the value of the charge on the plates becomes equal to 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 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 dielectric constant of the medium. It shows how many times the intensity of the interaction of charges separated by a dielectric decreases compared to plates in a vacuum. You can also say that this is one of the characteristics of the material.
If, upon accumulation of charge on the plates, the energy supply ceases, another phenomenon takes place. The voltage decreases and, as a result, the electric field decreases . Why?
Any material consists of atoms with electrons rotating around the nucleus. When an electric field appears, charge carriers are dispersed in each molecule according to the polarity of the external action — the so-called polarization forms, which forms a dipole. This is her electronic form. The material itself can consist of both polar and non-polar molecules. In the first case, the molecule is oriented according to the field (voltage), and since the dipoles are self-oriented, the relative permittivity is quite high. The value of their permeability often exceeds 100 units. In the second case (non-polar molecules), although due to the action of the field, dipoles are formed, 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 a gaseous substance always has a low permeability index due to the small number of molecules per unit volume, moreover, regardless of their natural structure.
For most common dielectric materials , permeability data are given in the corresponding tables, therefore, when performing calculations, there is no difficulty in determining the desired value. Interestingly, air has a permeability of 1 unit. This explains why various additional dielectric layers are used in capacitors - 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 capacity can be adjusted not only by the way the plates are arranged, but also by the material separating them. Champions among substances with high permeability are ceramics (about 80) and purified water from impurities (at least 81).