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An ideal gas is made of polyatomic molecules. Each of the molecules has three translational, three rotational and f number of vibrational modes. If the ratio of heat capacities $C_P/C_V$ of the gas is 8/7, then the value of f is:
Detailed Solution
Total degrees of freedom $F=\frac{2}{\gamma-1}$. Each vibrational mode contributes 2, so $6+2f=\frac{2}{\frac{8}{7}-1}=14 \Rightarrow 2f=8 \Rightarrow f=4$.