Question

briefly describe and explain the electronic polarization of non-metal materials or media upon light transmission, and elaborate its relationship with the electrical and magnetic properties in materials. Use schematics or equations if necessary

Answer 1

Light is an electromagnetic wave (EM), and the electric field of this wave oscillates perpendicularly to the direction of propagation. Many common light sources such as sunlight, halogen lighting, LED spotlights, and incandescent bulbs produce unpolarized light i.e. no particular direction of electric field. If the direction of the electric field of light is well defined, it is called polarized light. The most common source of polarized light is a laser.

Electric polarization, small relative shift of +Ve and -Ve electric charge in opposite directions within an insulator, or dielectric, induced by an external electric field. Polarizability is the relative tendency of a charge distribution, like the electron cloud of an atom or molecule, to be distorted from its normal shape by an external electric field, which may be caused by the presence of electric field component of an electromagnetic wave. This slight separation of charge makes one side of the atom somewhat positive and the opposite side somewhat negative. In some materials whose molecules are permanently polarized by chemical forces, such as water molecules, some of the polarization is caused by molecules rotating into the same alignment under the influence of the electric field.

One of the measures of polarization is electric dipole moment, which equals the distance between the slightly shifted centres of positive and negative charge multiplied by the amount of one of the charges. The electronic polarizability () is defined as the ratio of the induced dipole moment p of an atom to the electric field E that produces this dipole moment (p = E). Polarization P in its quantitative meaning is the amount of dipole moment p per unit volume V of a polarized material, P = p/V.

Polarization processes, including dielectric polarization and some other polarization mechanisms like Maxwell-Wagner-Sillars
(MWS) polarization and lattice polarization, have a close relationship with dielectric constant. Dielectrics are non-conducting substances. They are the insulating materials and are bad conductors of electric current. When we place a dielectric slab between the parallel plates of a capacitor, the ratio of the applied electric field strength to the strength of the reduced value of electric field capacitor is the Dielectric Constant. Dielectric polarization is derived from the local movement of bound charges and variation of dipole moment in the alternating EM field. The dielectric polarization mainly comes from molecular polarization, atomic polarization, ion polarization, space charge polarization and electron polarization.