Various body, as we all know, are divided on insulator (dielectric) and guides in their electrical properties.One of the features which have conductors in an electric field, is that the charges are balanced on the surface thereof, inside which the electric field is absent.How to explain this?
thing is that the conductors have special electrical charges.For example, metals, for example, are the bearers of such charges, the electrons that have lost touch with the atoms.They are called free electrons.
Such electrons in a conductor of metal, is placed in the electric field under the influence of forces of this field will move in a direction that is opposite to the electric field intensity.
Take the conductor in the electric field ABCD, which is placed in a uniform field of intensity, from left to right.
on the surface of AC conductor occurs excess negative charge and positive excess - to another DB.In this example, we see that the wires are electrified in the electric field.The charges that appear on the surface of the conductor, creating within him an additional electric field.His power lines have the opposite direction with respect to the lines of the main field.As a result, the tension of the main field at the conductor is reduced, ie,It weakens the force that acts on free electrons and causes them to move.The charges that are conductors in an electric field, the movement will stop when the resultant field strength within them becomes zero.
So at equilibrium the charge on the conductor inside the field is absent.Its absence can be used to protect the body from the influence of an external electric field.For this purpose it is sufficient to encircle the body of a thin conductive layer, for example, to place it in a box of metal.Inside this box fields will not.
To prove the fact that in a charged conductor is no electric field, in his experience, Faraday built a large wire cages, which is set in the insulators and recharged.Once inside the cell with hypersensitive electroscope, Faraday demonstrated that the inside is not any electrical power, although concentrated on the outer surface is very significant charge.This phenomenon is called electrification through influence or electrostatic induction.Its cause - effect of external electric field on the electrons in a conductor unoccupied.And the charges that have conductors in an electric field, called induced charges.
The phenomenon of electrification by influence explain the attraction between electrified and nenaelektrizovannymi bodies, as well as the transfer of electric charge by contact such bodies.
When electrified wire closer to easy, then it appears the induced charges of both signs.Thus, charges of opposite sign will be attracted to the body, and like charges will repel.Because like charges are on the side of the light guide, the more distant from the body, the resultant of these two forces is the force of attraction.Under the influence of this force is attracted to the light guide body.During the contact of the induced charge of opposite sign will be neutralized part of the charge is induced, which is equal to it in magnitude.In the light conductor will remain the same charge sign, and a body.
Due to the fact that a light conductor now has the same charge as the body, it will push away from it;what we observe experimentally.
conductors and dielectrics in the electric field have different properties.Thus, the dielectrics have virtually no free charges.When you place them in the phenomenon of electric field polarization.
