What is the permittivity of the medium

At school physics teacher in the classroom, talking about electrical phenomena, explained what the dielectric constant of the medium.In the future, if the main profession is not related to electrical engineering, the topic of safely forgotten.In this paper, we consider that lies behind this definition.

usually to explain the term "dielectric constant" is usually considered an example of a capacitor plate is flat.Imagine a simple condenser, which is in a vacuum.Define the value of the electric charge:

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

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

But capacitors separating plate medium may be not only vacuum, but also any other dielectric material.Obviously, in this case the dielectric constant of the medium is different from «Ev», and therefore the charge varies.If the capacitor is connected to a source of electromotive force, the value of the charge on the plates becomes Qz.The dielectric constant of the material is the ratio of the charge capacitor plates connected Qz to the charge in the case of vacuum Qv, ie

E = Qz / Qv.

Clearly, the dimension is absent.Powered condenser takes power from the source.

fact, it is the relative dielectric constant of the medium.It shows how many times the intensity of the interaction is decreased charges separated by a dielectric, as compared with plates in vacuo.Also, it can be said that this is one of the characteristics of the material.

If the accumulation of charge on the plates of the energy supply is stopped, there is a different phenomenon.Dropping the voltage, and consequently, the electric field intensity falls.Why is that?

Any material consists of atoms with electrons orbiting the nucleus.When the electric field distribution of the charge carriers takes place in each molecule according to the polarity of the external action - a so-called polarization, forming a dipole.This is an electronic form of it.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), as well as dipoles swiveling, the relative permittivity is rather high.Their permeability value often exceeds 100 units.In the second case (non-polar molecules), although due to the action of a dipole field and formed part of the energy is spent on maintaining their spatial configuration, so the permeability is negligible, and rarely more than 5 units.It should be noted that the gaseous substance always has a low rate of permeability due to a small number of molecules per unit volume, regardless of their natural structure.

for most common dielectric materials permeability data are given in the appropriate tables, so when performing the calculations do not arise difficulties in determining the desired value.Interestingly, the air has a permeability of 1 unit.This explains why in capacitors use a variety of additional dielectric layers - clay, mica, paraffin and so forth. All of these materials, having a higher permeability, increase the value of the accumulated charge on the plates.In other words, the capacitance can be adjusted not only in the way the location of plates and separating them pictures.Champion of high permeability materials are ceramics (80) and purified water from the impurities (at least 81).