The optical properties of plasmas with high densities and medium temperatures are analyzed by the use of a free electron model with Fermi-Dirac statistics. For the present collisional plasma the frequency of electron-ion collision is very large relative to the optical and infra-red frequencies. A quantum mechanical equation for the frequency of collisions is developed by the use of Fermi-Dirac statistics and Rutherford scattering theory. The validity of the Rutherford scattering theory is discussed. The influence of many weak collisions is taken into account by a Coulomb logarithmic function. The present analysis might have implication to stellar plasmas with medium temperatures for which Fermi-Dirac statistics is used. The relations between the present analysis and the stabilities of stars plasmas are discussed. The ratio between the radius and mass of star plasmas with the present densities and that of a typical white dwarf are discussed.
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