A substance having free particles with a charge moving orderly through the body due to the acting electric field is called a conductor in an electrostatic field. And the charges of particles are called free. Dielectrics, by contrast, do not have them. Conductors and dielectrics have different nature and properties.
Conductor
In an electrostatic field, conductors are metals, alkaline, acidic and saline solutions, as well as ionized gases. Carriers of free charges in metals are free electrons.
Upon entering a homogeneous electric field, where the metals are conductors without charge, movement will begin in a direction that is opposite to the field voltage vector. Accumulating on one side, the electrons will create a negative charge, and on the other side an insufficient number of them will cause the appearance of an excess positive charge. It turns out that the charges are separated. Uncompensated different charges arise under the influence of an external field. Thus, they are induced, and the conductor in the electrostatic field remains without charge.
Uncompensated charges
Electrification, when charges are redistributed between parts of the body, is called electrostatic induction. Uncompensated electric charges form their body, internal and external tensions are opposite to each other. Separating and then accumulating on opposite parts of the conductor, the internal field strength increases. As a result, it becomes zero. Then the charges are balanced.
Moreover, all uncompensated charge is outside. This fact is used to obtain electrostatic protection that protects devices from the influence of fields. They are placed in nets or grounded metal cases.
Dielectrics
Substances without free electric charges under standard conditions (that is, when the temperature is not too high and not low) are called dielectrics. Particles in this case cannot move around the body and only move slightly. Therefore, electric charges are connected here.
Dielectrics are divided into groups depending on the molecular structure. The molecules of the dielectrics of the first group are asymmetric. These include ordinary water, and nitrobenzene, and alcohol. Their positive and negative charges do not match. They act as electric dipoles. Such molecules are considered polar. Their electric moment is equal to the final value under all different conditions.
The second group consists of dielectrics in which the molecules have a symmetrical structure. This is paraffin, oxygen, nitrogen. Positive and negative charges have a similar meaning. If there is no external electric field, then the electric moment is also absent. These are nonpolar molecules.
Opposite charges in molecules in an external field have displaced centers directed in different directions. They turn into dipoles and get another electric moment.
The insulators of the third group have a crystalline structure of ions.
It is interesting how a dipole behaves in an external homogeneous field (after all, it is a molecule consisting of non-polar and polar dielectrics).
Any dipole charge is endowed with power, each of which has the same module, but a different direction (opposite). Two forces are generated having a rotational moment, under the action of which the dipole tends to rotate so that the direction of the vectors coincides. As a result, he receives the direction of the external field.
In a nonpolar dielectric there is no external electric field. Therefore, the molecules are devoid of electrical moments. In a polar dielectric, thermal motion is completely disordered. Because of this, the electric moments have a different direction, and their vector sum is zero. That is, the dielectric does not have an electric moment.
Dielectric in a uniform electric field
We put the dielectric in a uniform electric field. We already know that dipoles are molecules of polar and nonpolar dielectrics, which are directed depending on the external field. Their vectors are ordered. Then the sum of the vectors is not zero, and the dielectric has an electric moment. Inside it there are positive and negative charges that are mutually compensated and are close to each other. Therefore, the dielectric does not receive a charge.
Opposite surfaces have uncompensated polarization charges that are equal, that is, the dielectric is polarized.
If we take an ionic dielectric and place it in an electric field, then the crystal lattice of ions in it will slightly shift. As a result, an ionic type dielectric will receive an electric moment.
Polarization charges form their electric field, which has the opposite direction with the external. Therefore, the intensity of the electrostatic field, which is formed by charges placed in the dielectric, is less than in vacuum.
Conductor
A different picture will develop with the conductors. If conductors of electric current are introduced into an electrostatic field, a short-term current will appear in it, since the electric forces acting on free charges will contribute to the occurrence of motion. But everyone also knows the law of thermodynamic irreversibility, when any macroprocess in a closed system and movement should eventually end and the system be balanced.
A conductor in an electrostatic field is a body of metal, where the electrons begin to move against the lines of force and begin to accumulate on the left. The conductor on the right will lose electrons and get a positive charge. With the separation of charges, he will find his electric field. This is called electrostatic induction.
Inside the conductor, the electrostatic field is zero, which is easy to prove by moving from the opposite.
Features of charge behavior
The charge of the conductor accumulates on the surface. In addition, it is distributed in such a way that the charge density is oriented to the curvature of the surface. Here it will be more than in other places.
Conductors and semiconductors have the most curvature at the points of the corner, edges and roundings. A high charge density is also observed here. Along with its increase, tension is growing alongside. Therefore, a strong electric field is created here. A corona charge appears, due to which charges from the conductor flow together.
If we consider a conductor in an electrostatic field, from which the internal part has been removed, a cavity will be found. Nothing will change from this, because the field has never been, and never will be. Indeed, in the cavity it is absent by definition.
Conclusion
We examined conductors and dielectrics. Now you can understand their differences and features of the manifestation of qualities in similar conditions. So, in a uniform electric field, they behave very differently.