— physical quantity $\nu$, equal to the number of complete cycles of oscillations made per unit of time; one of the characteristics of a periodic oscillation process. From the period of oscillation $T$ are related $$\nu =\dfrac{ 1}{ T}$$ Unit O.f. periodic processes in SI — hertz (Hz).

— unit in integer times smaller system or Common Units of any physical quantity. For the formation of names decimal M.p. used consoles $deci \ldots\left(10^{-1}\right)$, $Santa \ldots\left(10^{-2}\right)$, $milli\ldots\left(10^{-3}\right)$, $miccro\ldots\left(10^{-6}\right)$, $nano\ldots\left(10^{-9}\right)$, $pico\ldots\left(10^{-12}\right)$, $femto \ldots\left(10^{-15}\right)$, $atto \ldots\left(10^{-18}\right)$. Eg., Microfarads $(uF)$ nanokulon $(nKl)$ femtometre $(FM)$ (com. Multiple Unit).

— the time period during which any deviation parameters of the system from its equilibrium value decreases $e$ times ( $e$ — base of natural logarithms).

— the largest time interval during which the main characteristics of the waves (amplitude, frequency, phase, polarization) remain constant or change a particular law; duration Zug waves. For white light T.of c. is $\sim 10^{-13} \mathrm{s}$ for laser $\sim 10^{-5} \mathrm{s}$ (see. as Coherence length, Coherence).

1. The average duration of unstable atomic nuclei or elementary particles; reciprocal constant decay.
2. Average length of stay quantum systems (atoms, molecules, etc.). In a state of constant energy; reciprocal transition probability.

As in 1) and 2) case L.t. equal to the period of time during which the number of quantum systems (atoms, molecules, atomic nuclei or elementary particles) that are in this state, decreases $e$ times ($e$ — base of natural logarithms).

— the main, along with space, form of existence of matter; quantity that describes the sequence of events (phenomena) that change each other, their sequence and relative duration. According to special relativity interval between two events Charles and the distance between the points (the scene) — relative, that have different meanings in different frames of reference (see. Own time, Own length). This suggests that the space-time value associated only with material objects and do not exist independently of them.

— part of the oscillation process between two points separated by time coherence.

— integral type $$ \oint_{L}(\vec{a}, \vec{d r})=\oint_{L}\left(a_{x} d x+a_{y} d y+a_{z} d z\right) $$ taken in a closed circuit some curve $L$. Stokes according to the Stokes formula, C.of v. $\vec{a}$ is the vector flow rot $\vec{a}$ (see.

— a chemical element, atomic number $40$, atomic weight $91.22$. Silver-white metal, density $6450\ \mathrm{kg} / \mathrm{m}^{3}$, melting point: $1852\ ^{\circ} \! {\mathrm{C}}$.

— a chemical element, atomic number $30$, atomic mass $65.38$. Metal bluish-white color, density $7130\ \mathrm{kg} / \mathrm{m}^{3}$, melting point: $419.5\ ^{\circ} \! {\mathrm{C}}$.