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JEE Main
Exam
JEE Main
Subject
Physics
Chapter
Kinetic Theory of Gases

JEE Main · Physics · Kinetic Theory of Gases

Under standard conditions, the density of a gas is ( (1400)/(1089)...

Under standard conditions, the density of a gas is (14001089 kg−\mathrmm−3\frac{1400}{1089} \mathrm{~kg} \mathrm{-} \mathrmm^{-3}) and the speed of sound propagation in it is (330  ms−1\mathrm{~ms}^{-1}), then the number of degrees of freedom of the gas molecules is

Options

  1. A2
  2. B7
  3. C5
  4. D3

Correct answer

C. 5

Step-by-step solution

Given, density of gas, (\rho=14001089 kgrho=\frac{1400}{1089} \mathrm{~kg}/ m3)speedofsound,(v=330\mathrm{m}^3) speed of sound, (v=330\mathrm{~m}//\mathrm{s})andunderstandardcondition,Pressureofgas,(p=1×105) and under standard condition, Pressure of gas, (p=1 \times 10^5\mathrm{~N}//\mathrm{m}^2) If (\gamma) be the ratio of CpandC_p andC_Vofagas,thenthespeedofsoundingasisgivenby(of a gas, then the speed of sound in gas is given by (v=γPρ or γPρ=v2γ=v2ρp=330×330105×14001089γ=1.4 So, γ=CpCV=1.4\begin{aligned} & \qquad v=\sqrt{\frac{\gamma P}{\rho}} \text { or } \frac{\gamma P}{\rho}=v^2 \\ & \quad \gamma=\frac{v^2 \rho}{p}=\frac{330 \times 330}{10^5} \times \frac{1400}{1089}\\ & \quad \gamma=1.4 \\ & \text { So, } \quad \gamma=\frac{C_p}{C_V}=1.4 \end{aligned}\$quad\left[∵\ggamma=1+2f Since, for diatomic gas, the volume of \begin{array}{l} \because \ggamma=1+\frac{2}{f}\\ \text { Since, for diatomic gas, the volume of } \end{array}\right] and γ is 1.4.  and  Hence, the degree of freedom for \begin{aligned} \text{ and } \gamma \text { is 1.4. }\\ \text{ and } \text { Hence, the degree of freedom for } \end{aligned}) So, (\gamma=\frac{C_p}{C_V}=$1.4) Since, for diatomic gas, the volume of \$(\left[\begin{array}{l} \because \ggamma=1+\frac{2}{f}\\ 1.4=1+\frac{2}{f}\\ \therefore f=5 \end{array}$$\right])(\gamma) is 1.4. Hence, the degree of freedom for diatomic gas is equal to 5.
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