Electrical dielectric constant

In the following discussion it should be noted that we use the same symbol, s, to represent both mechanical strain and the electrical dielectric constant. This is based on common terminology from the literature and should not cause the reader any difficulty, since both are used in differing contexts, s represents the complex dielectric constant, s the in-phase component or permittivity, and e" the out-ofphase component or dielectric loss factor. It is also important to note that the dielectric constant is not a constant but is strongly dependent on both frequency and temperature. 

Strong electrolytes are dissociated into ions that are also paired to some extent when tlie charges are high or the dielectric constant of the medium is low. We discuss their properties assuming that the ionized gas or solution is electrically neutral, i.e. 

Here a few core equations are presented from tire simplest tlieory for tire electric double layer tire Gouy-Chapman tlieory [41]. We consider a solution of ions of valency and z in a medium witli dielectric constant t. The ions... 

The dielectric constant is concerned with the electrical properties of a material. The dielectric constant for a solid is a 3 x 3 matrix with different components according to the Cartesian axes. These elements are given by ... 

The dielectric constant (permittivity) tabulated is the relative dielectric constant, which is the ratio of the actual electric displacement to the electric field strength when an external field is applied to the substance, which is the ratio of the actual dielectric constant to the dielectric constant of a vacuum. The table gives the static dielectric constant e, measured in static fields or at relatively low frequencies where no relaxation effects occur. 

Dielectric strength, kV mm Electrical Volume (dc) resistivity, ohm-cm Dielectric constant (60 Hz) Dielectric constant (10 Hz) Dissipation (power) factor (60 Hz) Dissipation factor (10 Hz) Mechanical Compressive modulus, 10Mb in-2 9.8-12 24-31 16-24 1014-1016 4.5-6.0 19 335-600 14 ... 

This result, called the Clausius-Mosotti equation, gives the relationship between the relative dielectric constant of a substance and its polarizability, and thus enables us to express the latter in terms of measurable quantities. The following additional comments will connect these ideas with the electric field associated with electromagnetic radiation ... 

Equations (10.17) and (10.18) show that both the relative dielectric constant and the refractive index of a substance are measurable properties of matter that quantify the interaction between matter and electric fields of whatever origin. The polarizability is the molecular parameter which is pertinent to this interaction. We shall see in the next section that a also plays an important role in the theory of light scattering. The following example illustrates the use of Eq. (10.17) to evaluate a and considers one aspect of the applicability of this quantity to light scattering. 

Electrica.1 Properties. The bulk electrical properties of the parylenes make them excellent candidates for use in electronic constmction. The dielectric constants and dielectric losses are low and unaffected by absorption of atmospheric water. The dielectric strength is quoted for specimens of 25 p.m thickness because substantially thicker specimens cannot be prepared by VDP. If the value appears to be high in comparison with other materials, however, it should be noted that the usual thickness for such a measurement is 3.18 mm. Dielectric strength declines with the square root of increasing... 

Electrical properties of acetal resin are collected in Table 3. The dielectric constant is constant over the temperature range of most interest (—40 to 50°C). Table 3. Electrical Properties of Acetal Resins... 

The magnitude of the induced dipole moment depends on the electric field strength in accord with the relationship = nT, where ]1 is the induced dipole moment, F is the electric field strength, and the constant a is caHed the polarizabHity of the molecule. The polarizabHity is related to the dielectric constant of the substance. Group-contribution methods (2) can be used to estimate the polarizabHity from knowledge of the number of each type of bond within the molecule, eg, the polarizabHity of an unsaturated bond is greater than that of a saturated bond. 

Electrical Resistance—Conductivity. Most fillers are composed of nonconducting substances that should, therefore, provide electrical resistance properties comparable to the plastics in which they are used. However, some fillers contain adsorbed water or other conductive species that can gready reduce their electrical resistance. Standard tests for electrical resistance of filled plastics include dielectric strength, dielectric constant, arc resistance, and d-c resistance. 

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