— elementary particles or quasiparticles with half-integer spin that obey Fermi-Dirac statistics. F. To include electrons, protons, neutrons, and others. (com. Boson).

Farms (Fm)

— obtained artificially radioactive chemical element, atomic number $100$, the mass number of the most stable isotope $257$. Named after the Italian. Physics Fermi.

Fermi-Dirac Statistics

— quantum statistics describing system behavior identical microparticles, which have half-integer spin. The main feature of AF-D with. is that every quantum state, which is described antisymmetric relative coordinate permutations particle wave function can be no more than two particles — fermions(see. Pauli principle). Proposed in $1926$ Italian. physicist Fermi $(1901 - 1954)$ and the English. physicist P. Dirac (b. $1902$) (com. Bose-Einstein statistics).

Fermi-Dirac Distribution

— the law of quantum statistics, which expresses the distribution of particle energy states in the system of fermions. According to F-Dr., The statistical equilibrium and the absence of interaction, the average number of particles and -th state with energy $\boldsymbol{\varepsilon}_{i}$ and equal $$ \left\langle n_{i}\right\rangle=\dfrac{1} {e^{\dfrac{\varepsilon_{i}-\mu}{ kT}}} $$ where $k$ — Boltzmann constant, $T$ — absolute temperature, $\mu$ - chemical potential of the system.

Fermat's Principle

— the guideline of geometrical optics, whereby light travels from one point to another in such a way to pass which required extreme (the smallest or largest) time compared to any other geometrically possible way between these points. Based on F. p. formulated fundamental laws of geometrical optics. Established French. mathematician P.Fermat (1601-1665).


— a set of properties and phenomena in magnetic substances and materials (ferromagnetic), with just the spontaneous magnetization of ferromagnets, but different origin. F. due to the presence of negative exchange interaction of electrons, resulting in a stable antiparallel orientation of the magnetic moments of the spins in the absence of a magnetic compensation latter that gives rise to spontaneous magnetization. F. sometimes defined as the magnetism that is not compensated.


— ferromagnets that possess semiconducting properties. Usually F. — zalizovuhletsevi alloys with the addition of silicon, manganese, phosphorus and othe elements.