JEE Main & Advanced Physics Kinetic Theory of Gases JEE PYQ-Kinetic Theory Of Gases

Two moles of helium are mixed with moles of hydrogen. If\[\frac{{{C}_{P}}}{{{C}_{V}}}=\frac{3}{2}\] for the mixture, then the value of n is     [JEE Online 15-04-2018 (II)]

A) 3/2

B)      2

C) 1

D)      3

Correct Answer: B

Solution :

[b] For a given mixture of gases,

\[({{n}_{1}}+{{n}_{2}})/(\lambda -1)={{n}_{1}}/({{Y}_{1}}-1)+{{n}_{2}}/({{Y}_{2}}-1)\]

Put \[{{n}_{1}}=2,Y=3/2,{{Y}_{1}}=5/3,{{Y}_{2}}=7/5\]

solving the required equation as

\[(2+n)/(3/2-1)=2/(5/3-1)+n/(7/5-1)\]

\[n=2\]