Dielectric permeability of air as physical quantity

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 it is possible to avoid the need to arrange additional insulating layers of some material around the conductor. Today we will talk about what is the dielectric constant of air. But first, perhaps, we'll start with the definition of what exactly is meant by the term "dielectric".

All substances, depending on the ability to conduct electric current, are conditionally divided into three large groups: conductors, semiconductors and dielectrics. The former exhibit minimal resistance to the directed passage through them of charged particles. The largest group is metals (aluminum, copper, iron). The second 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 vivid example is air.

What happens when the substance enters the zone of action of the electric field? For conductors, the answer is obvious - there is an electric current (of course, in the presence of a closed loop providing a "path" for particles). This is due to the fact that the way of interaction of charges varies. Absolutely other processes occur when the field is exposed to a dielectric material. When studying the interaction of particles with an electric charge, it was noted that the interaction force depends not only on the numerical value of the charge, but also on the medium that separates them. This important characteristic was called "dielectric permittivity of matter". 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 vacuum to the value in any medium. The physical meaning of the term "dielectric permittivity" is as follows: this value shows the degree of attenuation of the electric field by a dielectric material in comparison with vacuum. The reason for this phenomenon lies in the fact that the molecules of the material expend the field energy not on the conductivity of the particles, but on the polarization.

It is known that the dielectric constant of air is unity. Is this 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. Incidentally, it is from this table that the air value equal to one is taken. The dielectric constant of the air is almost eight times less than that of, for example, the getinax. Knowing this number, as well as the value of the charges and the distance between them, it is possible to calculate the force of their interaction, under the condition of separation by the air medium or the getinax plate.

The formula for the force is as follows:

F = (Q1 * Q2) / (4 * 3.1416 * E0 * Es * (r * r)),

Where Q1 and Q2 are charge values; E0 is the permeability in vacuum (a constant equal to 8.86 to the power of -12); Es is the permittivity of air ("1" or value for any other substance, according to the table); R is the distance between the charges. All dimensions are taken in accordance with the SI system.

Do not confuse two different concepts - the "magnetic permeability of air" and its dielectric permittivity. Magnetic is another characteristic of any substance, also representing a coefficient, but its meaning is another - the relationship between the field strength and the value of magnetic induction in a certain substance. In the formulas, a reference index is used-the magnetic permeability for pure vacuum. Both the first and second concepts are used to perform calculations of various electrical devices.