Consider the sound wave travelling in ideal gases of He, CH4, and CO2. All the gases have the same ratio P , where P is the pressure and is the density. The ratio of the speed of sound through the gases VHe : VCH4 : VCO2 is given by
- 75 : 53 : 43
- 53 : 43 : 43
- 53 : 43 : 75
- 43 : 53 : 75
Answer
(3) 53 : 43 : 75
Solution
Speed of sound in a gas (Laplace): v = P
Same P v
He (monatomic, 3 degrees of freedom): = 53
CH4 (non-linear polyatomic, 6 degrees of freedom): = 1 + 26 = 43
CO2 (linear molecule, 5 degrees of freedom, vibrations neglected): = 1 + 25 = 75
VHe : VCH4 : VCO2 = 53 : 43 : 75
Answer: (3)