Q 11-12-118JEE MainJEE Main 2020 (8 Jan, Shift 2)Easy
Consider a mixture of $n$ moles of helium gas and $2n$ moles of oxygen gas (molecules taken to be rigid) as an ideal gas. Its $\dfrac{C_P}{C_V}$ value will be:
Answer: (A) $\dfrac{19}{13}$
Helium (monatomic): $C_V = \tfrac{3}{2}R$, $C_P = \tfrac{5}{2}R$. Rigid oxygen (diatomic): $C_V = \tfrac{5}{2}R$, $C_P = \tfrac{7}{2}R$.
$$\gamma = \frac{n\cdot\frac{5}{2} + 2n\cdot\frac{7}{2}}{n\cdot\frac{3}{2} + 2n\cdot\frac{5}{2}} = \frac{\frac{5}{2}+7}{\frac{3}{2}+5} = \frac{19/2}{13/2} = \frac{19}{13}$$
Solution by Sreeraj P, M.Sc Physics