Dielectric susceptibility and permittivity

Science 2023

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Dielectric susceptibility and permittivity
Dielectric susceptibility and permittivity
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Phenomena such as dielectric susceptibility and permittivity are found not only in physics, but also in everyday life. In this regard, it is necessary to determine the meaning of these phenomena in science, their influence and application in everyday life.

Determination of tension

Intensity is a vector quantity in physics, which is calculated from the force that affects a single positive charge placed at the point of the field under study. After the dielectric is placed in an external electrostatic field, it acquires a dipole moment, in other words, it becomes polarized. To quantitatively describe the polarization in a dielectric, polarization is used - a vector physical index calculated as the dipole moment of the volume value of the dielectric.

dielectric susceptibility

The intensity vector after passing through the face between two dielectrics undergoes abrupt changes, causing interference during the calculation of electrostatic fields. In this regard, an additional characteristic is introduced - the vectorelectrical displacement.

Using the permittivity, you can find out how many times a dielectric can weaken an external field. In order to most rationally explain electrostatic fields in dielectrics, the electric displacement vector is used.

Basic definitions

The absolute permittivity of a medium is a coefficient that is included in the mathematical notation of Coulomb's law and the equation of the relationship between the electric field strength and electric induction. The absolute permittivity can be represented as the product of the relative permittivity of the medium and the electricity constant.

Dielectric susceptibility, called the polarizability of a substance, is a physical quantity that can be polarized under the influence of an electric field. It is also the coefficient of linear connection of the external electric field with the polarization of the dielectric in a small field. The formula for the dielectric susceptibility is written as: X=na.

In most cases, dielectrics have a positive dielectric susceptibility, while this value is dimensionless.

dielectric susceptibility and permittivity

Ferroelectricity is a physical phenomenon present in certain crystals, called ferroelectrics, at certain temperature values. It consists in the appearance of spontaneous polarization in the crystal even without an external electric field. The difference between ferroelectrics and pyroelectrics isthat in certain temperature ranges their crystal modification changes, and random polarization disappears.

Electricians in the field don't behave like conductors, but they share common characteristics. A dielectric differs from a conductor in the absence of free charged carriers. They are there, but in minimal quantities. In a conductor, an electron moving freely in the crystal lattice of a metal will become a similar charge carrier. However, electrons in a dielectric are bonded to their own atoms and cannot move easily. After the introduction of dielectrics into a field with electricity, electrization appears in it, like a conductor. The difference from a dielectric is that electrons do not move freely throughout the volume, as it does in a conductor. However, under the influence of an external electric field, a slight displacement of charges arises from inside the substance molecule: a positive one will be displaced in the direction of the field, and a negative one will be vice versa.

In this regard, the surface acquires a certain charge. The procedure for the appearance of a charge on the surface of a substance under the influence of electric fields is called dielectric polarization. If in a homogeneous and nonpolar dielectric with a certain concentration of molecules all particles are the same, then the polarization will also be the same. And in the case of the dielectric susceptibility of the dielectric, this value will be dimensionless.

Bound Charges

Due to the process of polarization, uncompensated charges appear in the volume of a dielectric substance, called polarization or bound. particles,having these charges, are present in the charges of molecules and, under the influence of an external electric field, are displaced from the equilibrium position without leaving the molecule in which they are located.

Bound charges are characterized by surface density. The dielectric susceptibility and permeability of the medium determines how many times the binding force of two electric charges in space is less than the same indicator in vacuum.

relationship between permittivity and susceptibility

The relative air susceptibility and permeability of most other gases under standard conditions is close to unity (due to the small plane). The relative dielectric susceptibility and permittivity in ferroelectrics is tens and hundreds of thousands on the separation surface of a pair of dielectrics with different absolute permittivity and susceptibility of the substance, as well as equal tangential strength components between them.

Among many practical situations, there is a meeting with the transition of current from a metal body to the surrounding world, while the specific conductivity of the latter is several times less than the conductivity of this body. Similar situations can occur, for example, during the passage of current through metal electrodes buried in the ground. Often steel electrodes are used. If the task is to determine the dielectric susceptibility of glass, then the task will be somewhat complicated by the fact that this substance has an ion-relaxation property, due to which a smallbelatedness.

On the boundary of a pair of dielectrics with different permeabilities in the presence of an external field, polarization charges appear with different indices with different surface densities. This is how a new condition for the refraction of the field line during the transition from a dielectric to another is obtained.

The law of refraction in the case of current lines in its form can be considered similar to the law of refraction of displacement lines on the verge of two dielectrics in electrostatic fields.

dielectric susceptibility formula

Each body and substance of the surrounding world has certain electrical properties. The reason for this lies in the molecular and atomic structure - the presence of charged particles that are in an interconnected or free state.

If the substance is not affected by an external field, then such parts are located, balancing each other, in the total total volume, without creating additional electric fields. If there is an application of electrical energy from the outside, a redistribution of charges will appear inside the existing molecules and atoms, which will lead to the appearance of its own internal field, which will be directed towards the outside.

When designating the applied external field as E0, and internal E', then the entire field E will be the sum of these values.

All substances in electricity are usually divided into:

  • conductors;
  • dielectrics.

This classification has existed for a long time, but is not entirely accurate, since science has long discovered bodies with new or combinedproperties of matter.

Conductors

As conductive substances can be media in which there are free charges. Metals are often considered such matters, since their structure implies the constant presence of free electrons that can move inside the entire cavity of the substance. The dielectric susceptibility of the medium allows you to be a participant in the thermal process

permittivity and susceptibility of matter

If the conductor is isolated from the influence of an external electric field, then a balance appears inside it between positive and negative charges. This state immediately disappears when a conductor appears in an electric field, which redistributes charged particles with its energy and provokes the appearance of unbalanced charges with a positive and negative value on the outer surface

This phenomenon is called electrostatic induction. The charges that appeared under its action on the surface of the metal are called induction charges.

The inductive charges that have arisen in the conductor create their own field, which compensates for the influence of the external field inside the conductor. In this regard, the indicator of the total total electrostatic field will be compensated and equal to 0. The potentials of each point inside and outside are equal.

This result indicates that inside the conductor (even with an external field connected) there is no difference in potentials and no electrostatic field. This fact is used in shielding due to the usemethod of electro-optical protection of a person and electrical equipment sensitive to fields, especially high-precision measuring instruments and microprocessor technology.

dielectric susceptibility and permeability of the medium

There is also a connection between permittivity and susceptibility. However, it can be expressed using a formula. So the relationship between the dielectric constant and the dielectric susceptibility has the following notation: e=1+X.

ESD principle

With the help of shielding, clothes and shoes made of materials with conductive properties, including hats, are used in the energy sector for the safety of personnel working in conditions of high tension provoked by high-voltage devices. The electrostatic field does not penetrate inside the conductor, because when the conductor is introduced into the electric field, it will be compensated by the field that arises due to the movement of free charges.

Dielectrics

This name belongs to substances that have insulating qualities. They contain only interconnected charges, not free ones. Each positive particle in them will be bonded to a negative one inside an atom with a common neutral charge without free movement. They are distributed from inside the dielectrics and cannot change their position under the influence of external fields. At the same time, the dielectric susceptibility of the substance and the resulting energy still entail certain changes in the structure of the substance. From inside the atom and molecule, the ratio changespositive and negative charges of the particle, and extra unbalanced interconnected charges appear on the surface of the substance, creating an internal electric field. It is directed towards the tension applied from outside.

This phenomenon is called dielectric polarization. It can be characterized by the fact that an electric field arises from inside the substance, caused by the influence of external energy, but weakened by the counteraction of the internal field.

Types of polarization

Inside dielectrics, it can be represented by two types:

  • orientation;
  • electronic.

The first type also has an additional name - dipole polarization. This property is inherent in dielectrics with displaced centers at the positive and negative charge, which create molecules from small dipoles - a neutral combination of a pair of charges. This phenomenon is typical for a liquid, hydrogen sulfide, carried nitrogen.

Without the influence of an external electric field in these substances, molecular dipoles are oriented randomly under the influence of existing temperature changes, when an electric charge does not appear on the outside of the dielectric.

determine the dielectric constant of glass

This picture changes under the action of energy applied from outside, when the dipoles do not change their orientation much and uncompensated macroscopic bound charges appear on the surface, creating a field with the opposite direction to the field applied from outside.

Electronic polarization, elasticmechanism

This phenomenon occurs in non-polar dielectrics - materials of a different type with molecules in which there is no dipole moment, which, under the action of an external field, is deformed so that only positive charges are oriented in the direction of the external field vector, and negative charges - in the opposite direction.

As a result, each molecule functions as an electric dipole oriented along the axis of the applied external field. Similarly, an own field appears on the outer surface, which has the opposite direction.

Polarization of a non-polar dielectric

For these substances, the change of molecules and the subsequent polarization from the influence of the field outside is not dependent on their movement under the influence of temperature. Methane CH4 can be used as a nonpolar dielectric. The numerical indicators of the internal field for both dielectrics will initially change in magnitude in proportion to the change in the external field, and after saturation, effects of a nonlinear type appear. They appear when each molecular dipole has lined up along the lines of force near polar dielectrics, or changes in non-polar substances have occurred, caused by a strong deformation of atoms and molecules from a large amount of energy applied from outside. In practical cases, this happens extremely rarely.

Dielectric Constant

Among insulating materials, a serious role is given to electrical indicators and such a characteristic as dielectric constant. Both are judged by two different characteristics:

  • absolute value;
  • relative indicator.

The term absolute permittivity of a substance refers to the mathematical notation of Coulomb's law. With its help, the relationship between the induction vector and the intensity is described in the form of a coefficient.

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