Question

The ratio of specific heats of a gas is $9/7$, then the number of degrees of freedom of the gas molecules for translational motion is :

• A. $7$
• B. $3$
• C. $6$
• D. None

Answer 1

Answer: (B)

$3$

Given,

$\gamma =\frac{9}{7}$

and we know that, $\gamma =1+\frac{2}{f}$

where $f=$ degree of freedom

$\frac{9}{7}=1+\frac{2}{f}$

$\frac{2}{7}=\frac{2}{f}$

$f=7$

The total degree of freedom is $7$, but the maximum degree of freedom for translational motion is $3$ and remaining $4$ are for vibrational and rotational motion.

The correct option is B.