Hall effect
When the current direction of a stationary current-carrying conductor placed in a magnetic field is different from that of the magnetic field, an electromotive force difference occurs between the two surfaces of the current-carrying conductor parallel to the current direction and the magnetic field direction, which is called Hall effect. ? The formed electric field EH is called Hall field. The physical parameter representing Hall field is called Hall coefficient, which is defined as: RH=EH/JxB0? Hall coefficient RH has the following expression: Hall coefficient, which indicates the strength of Hall effect, is only related to the density of free electrons in metals.
polarization
Spontaneous polarization: this polarization state is not caused by external electric field, but by the internal structural characteristics of the crystal. Each unit cell in a crystal has an inherent electric dipole moment.
Electron displacement polarization: polarization formed by the displacement of the electron cloud around the atom relative to the nucleus under the action of electric field.
Ion displacement polarization: under the action of electric field, the movement of ions out of equilibrium position is equivalent to forming an induced dipole moment.
Polarization frequencies are as follows
Polarization of dielectric: under the action of electric field, the bound charge in the dielectric is elastically displaced and the dipole is oriented. Basic way:
Electrode polarization: 1) electron polarization (electron displacement polarization): under the action of e, the center of the electron cloud around the atom is displaced relative to the nucleus, forming an induced electric moment and polarizing the medium.
Fast formation (10-14 ~10-16s), elastic reversibility, and no energy consumption in the polarization process. It exists in all dielectrics, but only neutral gases, liquids and a few nonpolar solids exist in dielectrics with this polarization.
2) Ion polarization (ion displacement polarization): In ionic crystals, apart from the displacement polarization of electrons in ions, the polarization caused by the relative displacement of positive and negative ions under the action of E can be divided into:
A. Ion elastic displacement polarization: In the crystal composed of ionic bonds, the binding force between ions is very strong, the ion displacement is limited, and the polarization process is very fast (? 10-12 ~10-13s) has no energy consumption and is reversible.
? 3) Dipole polarization (steering polarization of inherent electric moment): When there is E, dipoles tend to arrange along the direction of electric field, resulting in macroscopic electric moment and polarization. It takes a long time (10-2 ~10-10s), which is irreversible and consumes energy. 4) Space charge polarization: In some dielectrics, there are mobile ions, and it takes the longest time (10-2s) for the positive and negative ions to separate and polarize under the action of E. Photoluminescence? The electrons in the material are excited to a high energy state by light irradiation, resulting in luminescence.
Cathode ray luminescence? In the process of bombarding materials with high-energy electrons, the multiple scattering collisions of electrons inside the materials make various luminescent centers in the materials excited or ionized to emit light.
Electroluminescence? Light emission is caused by applying an electric field to an insulated light emitter or injecting electrons into a semiconductor conduction band from an external circuit.