Electric charge displacement

The observed dielectric constant M and the dielectric loss factor k = k tan S are defined by the charge displacement characteristics of the ceramic ie, the movement of charged species within the material in response to the appHed electric field. Discussion of polarization mechanisms is available (1). 

An electric field induces a polarization of the charge within a single molecule by the instantaneous displacement of the electrons with respect to the nucleus. In this manner an induced dipole and, hence, a dipolar moment, p, are generated. When the applied field is weak, the induced charge displacement is proportional to the strength of the field ... 

We observe that in the alcohol molecule the O—H and C—OH bonds are polarized, the center of gravity of the electron cloud in the former case being displaced towards the 0 atom and in the latter case towards the OH group. Hence, when these bonds are broken by the field of the lattice (dissociation at adsorption, see Sec. III,C), electrically charged formations will arise on the surface, as depicted in the right-hand side of Fig. 17a and, respectively. Fig. 18a. 

In addition to electric charge between particles other factors are in some cases operative in preventing actual contact, thus the medium may be strongly adsorbed by the surface, and the thin film may not readily be displaced on collision of the two neutral particles, in other cases a tough elastic film may be formed, possessing definite mechanical strength and necessitating a violent impact to ensure rupture. 

The conductivity of PVC and PVA increases when these polymers are heated. The centers of positive and negative electric charges of nonpolar polymers coincide in the absence of an electric field. However, when a polymer is placed in an electric field, the positive and negative charges in the polymer are displaced, and it becomes a temporary dipole. 

This description of antennas may seem more appropriate to a discussion of radio or television waves. We must realize, however, that at the molecular level dipoles behave exactly like antennas. Since molecules are made up of charged parts, a dipole moment /x is induced by the electric field of the radiation in any material through which radiation passes. In this discussion, the dipole moment equals the product of the effective charge displaced by the field and its distance of separation from the opposite charge. In SI, pi has units C m. We consider isotropic materials characterized by a polarizability a. As the name implies, this property measures the ease with which charge separation —polarity —is induced in a molecule by an electric field. For isotropic substances, the dipole moment and the field are related by the expression... 

Let us illustrate the simplest response approach by an example representing the many-particle system counterpart of Eqn. (5.1). Let F(t) stem from an (periodic) electric field E(t) acting upon an electric charge. The response of a dielectric with permittivity to the field E is the displacement... 

In some crystals the presence of ions can be demonstrated without making use of destructive techniques. These crystals produce an electric effect when they are compressed. Due to this pressure, ions are displaced and this displacement of electrical charges is a voltage. The deformation in a crystal leads to movement of both negative and positive ions. When these both move equally far and in the same direction, the result is no net voltage. A crystal will only exhibit piezoelectricity when the positive and negative ions cover a different distance once subjected to pressure. What exactly take place in such a crystal is illustrated in figure 11.4.26... 

The definition of electric charge density in Eq. (76) agrees with our opinion that 0 in Maxwell s equations represents charge neutrality (see Section HI) the simplest case is 5+ + S = 0. Also note that X/ defined by Eq. (74) is independent of pe thus allowing for the existence of a displacement current in the absence of electric charge, as also discussed in Section HI. 

A dielectric is a substance in which an electric field gives rise to no net flow of electric charge. This is due to the reason that electrons in a electric are tightly held by individual atoms. However, under the effect of applied field displacement of charges takes place, resulting in the creation of dipoles. 

The ease of time-varying charge displacement, measured as the time-dependent dielectric or magnetic permittivity (or permeability), is expressed by the dielectric function e and magnetic function /x. Both e and // depend on frequency both measure the susceptibility of a material to react to electric and magnetic fields at each frequency. For succinctness, only the dielectric function and the electrical fluctuations are described in the rest of this introductory section. The full expressions are given in the application and derivation sections of Levels 2 and 3. 

Recognize causality. An effect (charge displacement) must come after a cause (applied electric field). 

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