Dielectrics in an electric field

Dielectrics in an electric field behave according to their internal structure. They are also called nonconductors, since, as is known, they are substances that do not conduct almost electric current. They do not contain free charge carriers, which would be able to move inside this dielectric.

A molecule is the smallest particle of a substance that retains its chemical properties. It, in turn, itself consists of atoms with a positively charged core and negatively charged electrons. Molecules in general are neutral. As the theory of covalent bonds says , one or several pairs of electrons formed in them, becoming common for connecting atoms, ensure the stability of molecules.

For each type of charge - positive (nuclei) and negative (electrons) - there is a point, which is like for them a "center of gravity" (electrical). These points are called the poles of the molecule. In the case of coincidence in the molecule of electrical centers of gravity of opposite charges: positive and negative - it will be nonpolar (not having a dipole moment).

The structure of the molecule can be asymmetric, say, there may be two heterogeneous atoms in it, then to some extent the displacement of the total pair of electrons in the direction of one of the atoms must occur. It is clear that in this case the uneven distribution of unlike charges (positive and negative) inside the molecule will lead to a mismatch of their electrical centers of gravity. The resulting molecule is called polar or has a dipole moment.

The main property of dielectrics is their ability to polarize.
Dielectrics in an electric field are polarized. This means that in their atoms the electrons begin to move along elongated orbits. As a result, some of their surfaces turn out to be negatively charged, others - positively. Thus, an electric field appears in dielectrics, which, accordingly, is called internal. That is, dielectrics are simultaneously affected by electric fields (external and internal), which are opposite in this case.

The resulting electric field has a strength equal to the difference in the strengths of the larger and smaller of the fields. It should be noted that the field strength in the dielectric, regardless of its type, is always less than the electric field strength that caused its polarization.

The intensity of polarization is directly proportional to the dielectric constant of the dielectric. The smaller it is, the less intense is the polarization in the dielectric and the stronger the electric field in it.

Charges appear not only on the surface, but also at the ends of the dielectric, but their transition upon contact with the electrode is impossible, since a nonconductor is attracted to the electrode by Coulomb forces.

Dielectrics in the electric field, if it is strong and its tension can be increased, will begin to break through at certain values of the tension, that is, electrons will begin to break away from the atom. This will lead to a process of ionization of dielectrics, as a result of which they become conductors.

The magnitude of the strength of the external field, which leads to breakdown of the dielectric, is called its breakdown intensity. And the corresponding limiting voltage at which the dielectric breaks through is the breakdown voltage. Another name for the limiting voltage is known - the dielectric strength.

It should be noted that only dielectrics in an electric field have an internal field, which basically disappears if the external one is removed.