Question

The ratio $\left(v\right)$ of velocities of sound in dry air and humid air is

• A. $v<1$
• B. $v>1$
• C. $v=1$
• D. Zero

Answer 1

The correct option is A $v<1$

Because water molecules have less mass than the average air molecules $\left(N_2\right(28\text{amu}),$ while water $H_{2}O\left(18amu\right)).$ But It will happen if and only if the pressure is unchanged. Given that dry and humid air are both under the same pressure then we have smaller density for humid air.
And velocity of sound waves$,v,$ in a medium is given by,

$v=\sqrt{\frac{\gamma E}{d}}$, here $\gamma =\frac{C_P}{C_V}$,

$E$ is elasticity of the medium, and $d$ is the density.

Since, density of air decreases with humidity increases. therefore velocity of sound increases in humid air.
Option "A" is correct.