The dielectric constant

protection click fraud

level polarizability is characterized by a special substance quantity, which is called the dielectric constant.Consider what the value is.

assume that the intensity of the uniform field between the two charged plates in a vacuum is E₀.Now fill in the gap between any dielectric.Electric charges that will appear on the boundary between the dielectric and conductor thanks to its polarization, partially neutralized the impact of the charges on the plates.The intensity of the E field will be less tension E₀.

Experience shows that the sequential filling of the gap between the plates is dielectrics, the value of the field intensity will be different.Therefore, knowing the ratio of the voltage electric field between the plates in the absence of a dielectric E₀ and in the presence of the insulator E, it is possible to determine the polarizability, ie,its permittivity.This value is usually denoted by the Greek letter reversed ze (epsilon).Consequently, we can write:

reversed ze = E₀ / E.

The dielectric constant shows how many times the intensity of the field of data charges in the dielectric (uniform) will be less than in a vacuum.

Reduction of forces between charges due to the processes of polarization of the medium.In an electric field, the electrons in the atoms and molecules are reduced with respect to ions, and a dipole moment.Iethose molecules that have a dipole moment (particularly water molecules), are oriented in an electric field.These moments create their own electric field that counteracts the field that caused their appearance.As a result, the total electric field is reduced.In small fields this phenomenon is described by the concept of the dielectric constant.

Below is the permittivity of vacuum various substances:

Air ................................. .... 1,0006

Paraffin .............................. ....2

Plexiglas (Plexiglas) ...... 3-4

Ebonite ................................. .. ... 4

Porcelain ................................. .... 7

Glass .............................. .. ...... .4-7

Mica ................................. .. ... .4-5

Silk natural ............ 4-5

Slate .............................. 6-7

Amber.............................. ... ...... 12,8

Water .................................... ... ... .81

The values ​​of permittivity materials are to the ambient temperaturein the range 18-20 ° C.For example, the dielectric constant of solids varies slightly with temperature, exceptions are ferroelectrics.

On the contrary, it decreases gas because of higher temperatures and increases due to the increased pressure.In practice, the dielectric constant of air is taken as one.

impurities in small amounts have little effect on the level of dielectric constant fluids.

If any two point charge placed in the dielectric strength of the field generated by each of these charges at the point where another charge decreases reversed ze time.It follows that the force with which these charges interact with one another in reversed ze times smaller.Therefore, Coulomb's law for charges placed in the dielectric is given by:

F = (q₁q₂) / (ԑₐr²).

SI:

F = (q₁q₂) / (4πԑₐr²),

where F - is the force interaction, q₁ and q₂, - the value of the charges reversed ze - absolute dielectric constant of the medium, r - the distance between the point charges.

reversed ze numerical value can be shown in relative terms (in relation to the absolute value of the dielectric constant of the vacuum ԑ₀).The amount reversed ze = ԑₐ / ԑ₀ called relative permittivity.It reveals how many times the interaction between the charges in an infinite homogeneous medium is weaker than in a vacuum;reversed ze = ԑₐ / ԑ₀ often referred to as complex dielectric constant.The numerical value of ԑ₀ and its dimension depending on which system of units is selected;and the value of reversed ze - independent.Thus, the system ԑ₀ esu = 1 (this fourth main unit);SI permittivity of free space expressed:

ԑ₀ = 1 / (4π˖9˖10⁹) farad / meter = 8,85˖10⁻¹² f / m (in this system ԑ₀ is a derivative value).