What is the physical meaning of dipole moment (not the distance between the equal and opposite charges multiplied by the magnitude of charge)? Is it considered for metals?
Sir Peter Kapusta, I understood from certain textbooks that dipole moment is nothing but a short distance interaction between two equal and opposite charges. But, what is its physical meaning? Like for curl = circulation, divergence = outward flow, what does dipole moment stand for?
Let alone electrostatics hardly helpful in metal science (sorry). What does matter here, it is the dipole moments of internal FORCES that is a characteristic of a point-like STRESS SOURCE. In particular the stress field by an inclusion (with uniform plastic strain inside like in Eshelby's model) is expressed through the corresponding dipole moment of fictitious interfacial forces, which in turn equals stress inside it x its volume. When considering various (complex) point defects on the atomic scale, this trick is seemingly the only bridge (transition) to asymptotic mechanistic stress field. Google around point defects, "Kanzaki forces", etc. If you steel need visualization, the dipole moment of forces is a measure for effects of internal "compressed spring" constrained by surrounding.
In a dielectric, won't the charges orient in a fashion to oppose the applied electric field and cancel the field inside just like a metal? The fields inside the dielectric add up vectorially?
Well, you should know from school (University anyway) that inside dielectrics an applied electric field does not vanish (like in metals) but weakens to a certain degree and this effect is characterized by a certain material constant. In principle, the latter may be tensor (not scalar) i.e. the resulting field may have a particular direction different from the applied one.
It is interesting, especially for comparisons with magnets, to study the properties of an electric dipole. In an electric field, the dipole tends to move in a direction parallel to the field. The electric dipole moment can be considered as a vector attached to the dipole, whose direction and sense are those of the line joining negative charge to the positive charge.
Many molecules can be considered as electric dipoles. These molecules are broadly neutral, but have a difference in electronegativity which generates a permanent dipole moment. This moment is a vector that we know only experimentally determine the module. Despite the difficulty of the measures, the value of the dipole moment of a molecule is a piece of information in the study of its structure. Thus, the zero value of the dipole moment of Carbon dioxide CO2 involves a symmetrical linear structure. Conversely, the value of the dipole moment of the oxygenated water H2O2 (p = 2.10 D) prohibits symmetrical structure and involves a non-planar structure...
If you speak the French language, you can take a look at my books of electrostatics.
" In solids, rotation is impossible or strongly hindered."
"...Well, you should know from school (University anyway) that inside dielectrics an applied electric field does not vanish (like in metals) but weakens to a certain degree."???
Then how does field inside the dielectric increase by D=ε0*E+P?
I agree with all authors, but I want to deal with the second part of your first question. As said by A.A. Zisman , the electric field vanishes inside a metal. Indeed, this is a well known property of a conductor in electrostatic equilibrium. However, It is worth pointing out that adsorption of atoms or molecules on a metallic surface changes the dipole layer and hence the work functions: 1) electronegative adsorbates (e.g., O, C, and S) increase the work function and 2) electropositive adsorbates (e.g., Na, K, and Cs) decrease the work function. In these cases, dipole moment is considered for metals, not for the bulk, but for the contaminated surface.
On the other hand, a dielectric subjected to an electric field acquires a macroscopic dipole moment.
Sir Peter Kapusta: "...The equation you posted is the definition formula of electric displacement field in Maxwell theory. It does not tell that the "field inside the dielectric increase""
It is said in Sadiku text book that "...The net effect of E on the dielectric is to increase D inside it by P. Due to application of E to the dielectric material, the flux density would be greater than in free space."
No, I have a confusion on the permittivity of metals. As permittivity is decided by electric susceptibility (Xe = er-1), Xe is a measure of how much a material can be polarized, er being dielectric permittivity of metal.
Now, since in metals a sea of electrons exist and with an application of electric field charges separate by a large distance (my imagination), there is no net dipole moment in a metal. Hence, there is no polarization for metals. Thus, Xe = 0 and er = 1.
But, permittivity is the resistance to the formation of electric field in it. And metals offer infinite resistance to the formation of electric field as they screen the external fields. This means that permittivity of a metal is infinity.
COnFusiON!
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