As you know, the air around us is a combination of several gases, so it is a good dielectric. In particular, due to this, in many cases, the need to organize additional insulating layers of some material around the conductor is avoided. Today we will talk about what is the dielectric constant of air. But first, perhaps, we’ll start by defining what exactly is meant by the term “dielectric”.
All substances, depending on their ability to conduct electric current, are conventionally divided into three large groups: conductors, semiconductors, and dielectrics. The former provide minimal resistance to the directed passage of charged particles through them. Their largest group is metals (aluminum, copper, iron). The latter conduct current under certain conditions (silicon, germanium). Well, the electrical resistance of the third is so great that the current does not pass through them. A striking example is air.
What happens when a substance enters an electric field? For conductors, the answer is obvious - an electric current arises (of course, in the presence of a closed circuit, providing a "path" for particles). This is due to the fact that the way the interaction of charges changes. Completely different processes occur when a field acts on a dielectric material. When studying the interaction of particles with an electric charge, it was noted that the strength of the interaction depends not only on the numerical value of the charge, but also on the medium separating them. This important characteristic is called the "dielectric constant of a substance." In fact, it is a correction factor, since it has no dimension. It is defined as the ratio of the value of the interaction force in a vacuum to the value in any medium. The physical meaning of the term "dielectric constant" is as follows: this value shows the degree of attenuation of the electric field by the dielectric material compared to vacuum. The reason for this phenomenon lies in the fact that the molecules of the material spend the field energy not on the conductivity of the particles, but on the polarization.
It is known that the dielectric constant of air is equal to unity. Is it a lot or a little? Let's figure it out. Now there is no need to independently calculate the numerical value of permeability for most common substances, since all these data are given in the corresponding tables. By the way, it is from such a table that the air value equal to unity is taken. The dielectric constant of air is almost 8 times less than that of, for example, getinaksa. Knowing this number, as well as the value of the charges and the distance between them, it is possible to calculate the strength of their interaction, provided that the air is separated by a getinax plate.
The formula for strength is as follows:
F = (Q1 * Q2) / (4 * 3.1416 * E0 * Es * (r * r)),
where Q1 and Q2 are the values of the charges; E0 - permeability in vacuum (constant equal to 8.86 in the degree of -12); Es - dielectric constant of air (“1” or value for any other substance, according to the table); r is the distance between charges. All dimensions are taken in accordance with the SI system.
Two different concepts should not be confused - “magnetic permeability of air” and its dielectric constant. Magnetic is another characteristic of any substance, which is also a coefficient, but its meaning is different - the relationship of the field strength and the value of magnetic induction in a particular substance. The formulas use a reference indicator - magnetic permeability for a clean vacuum. Both the first and second concepts are used to perform calculations of various electrical devices.