Question

In a mixture of gases, the average number of degrees of freedom per molecule is 6. The rms speed of the molecules of the gas is c. The velocity of sound in the gas is 

(a) c/√2 

(b) 3c/4 

(c) 2c/3 

(d) c/√3 

Answer 1

Correct Answer is: (c) 2c/3 

γ = 1 + 2/f = 1 + 2/6 = 4/3

C = √(3p/ρ) and v = √(γp/ρ)

∴ v/c = √γ/3 = √4/9 =2/3.