The isentropic exponent and relation for monoatomic plasmas

The different values of the isentropic exponent and of the exponent of the isentropic relation in case of plasmas is discussed. This difference is explained by how ionisation is included in the derivation of the exponent. The plasma is called in a fixed state, or frozen state, when ionisation (or recombination) will not occur. The consequence of two different exponents are discussed with respect to the Mach number and to plasma expansions.