الفهرس 
CLASSICAl METHOOSOnly 14 pages are availabe for public view
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Abstract
The classical statistical mechanics faile to provide an adequate description of the behavior of gases at low temperatures. Such failure is due to some effects which appear at low temperatures when gases are degenarate and do not behave according to classical laws. In this case we have to apply the quantim statisticallmechanics and that is why we call these effects the quantum effects which can be classified into two : 1- Diffraction effects, which result from the wave nature of the molecules. 2- Symmetry effects, which are spin effects and result from the choice of one of the two quantum statistics applied to the molecules according to their spin.