JEE MAIN - Physics (2021 - 17th March Evening Shift - No. 7)

If one mole of the polyatomic gas is having two vibrational modes and $$\beta$$ is the ratio of molar specific heats for polyatomic gas $$\left( {\beta = {{{C_P}} \over {{C_V}}}} \right)$$ then the value of $$\beta$$ is :
1.02
1.35
1.2
1.25

Explanation

For polyatomic gas molecule has 3 rotational degrees of freedom, 3 translational degrees of freedom, and 2 vibrational modes.

So, number of vibrational degrees of freedom = 2 $$ \times $$ 2 = 4

Degree of freedom of polyatomic gas

f = T + R + V

f = 3 + 3 + 4 = 10

$$\beta = 1 + {2 \over f} = 1 + {2 \over 10}$$

$$\beta = {{12} \over 10} = 1.2$$

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