DIELECTRIC IN AN ELECTRIC FIELD – FIZIKATYT
The dielectric, when exposed to an electric field, is polarized: electric charges are induced on its surfaces. If the electric field is increased, then at a high voltage breakdown of the dielectric occurs, its structure changes, and an electric current appears.
What is polarization?
When an external electric field acts on an atom, its electron cloud changes its shape and shifts towards positive electric charges. The atom becomespolar: it has positive and negative poles.
A negative charge is formed on the crystal surface facing the positive electrode. On the opposite surface facing the negative electrode, the charge is positive.
The number of free charge carriers is growing rapidly, an avalanche effect occurs. In this case, electrons rush from the negative electrode to the “positive” side of the body, compensating for the loss of intrinsic charge carriers in the sample. Conductive channels are formed in the dielectric, a large current flows through them, from which the temperature rises greatly; the substance is destroyed.
The results of such phenomena are broken capacitors in radio equipment, destroyed insulation in electrical devices.
The brightest, familiar manifestation of dielectric breakdown is lightning discharges. But what is the source of electrical voltage during a thunderstorm? Where does the external electric field in the sky come from? Here another property of dielectrics is manifested: they are capable of creating and accumulating significant amounts of free charge carriers themselves.
The field intensity is especially strong near pointed towering objects: masts, mountain peaks, electrical supports “attract” lightning. A breakdown of the dielectric occurs, with the formation of an avalanche channel in the air; a strong current flows through this channel.
Dangerous prejudice associated with electrical discharges
An avalanche effect of an electric discharge can be provoked not only by a metal column, but also by a radio signal source. It is dangerous to use your cell phone if a thunderstorm is coming.