ÓÄÊ 536.7..621.391; PACS 05.45, 07.50.H, 72.70
**Microscopic parameters of a stochastic system and variance of physical quantity**
(ideal gas, electric current, thermal radiation of a black body)
** E. A. Salkov**
*Institute of Semiconductor Physics, NAS Ukraine, 45 prospekt Nauki, Kyiv, 252028, Ukraine *
**Abstract.** It is shown that the variance of a random physical quantity F can be expressed and directly calculated with the help of a microscopic parameter which under certain conditions may be called the invariable intrinsic “micro-quantity of chaos” (MQC). MQC is a self-sufficient concept that characterises a physical system or a stochastic process. The following statement is proposed: if a random physical quantity F is additive and its fluctuations are statistically independent, then its variance <DF2> can be expressed as the product of the mean value <F> and the corresponding value of the MQC = qF, i.e., <DF2> = qF.<F>. Physical situations are considered in the frame of which this statement has been substantiated. The MQC concept is demonstrated for fluctuations in the ideal gas. Expressions of MQC are proposed for fluctuations of black body radiation, electrical and photocurrents. Arguments for usefulness of the MQC concept are presented.
**Keywords**: random physical quantity, macro parameter, micro parameter, variance, electric current, radiation, thermal noise, shot noise, generation-recombination noise.
Paper received 13.07.98; revised manuscript received 10.10.98; accepted for publication 28.10.98.
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