Question

The velocity of sound in air is not affected by change in
(A) the moisture content of the air.
(B) the temperature of air.
(C) the atmospheric pressure.
(D) the composition of air.

Answer 1

Hint
We know that sound is a mechanical wave that results from the back and forth vibration of the particles of the medium through which the sound wave is moving. The motion of the particles is parallel, or sometimes anti-parallel to the direction of the energy transport. This is what characterizes sound waves in air as longitudinal waves. Sound waves fall into three categories: longitudinal waves, mechanical waves, and pressure waves.

Complete step by step answer
The speed of sound depends on the temperature of the medium. The formula relating the speed of sound and temperature is given:
$\text{v}=331+0.6\times \text{T}$
where is temperature in absolute scale and is the velocity of the sound which is in .
Humidity also has a little effect on the speed of sound because it increases the density of air lowering the speed. Air pressure has no effect at all in the speed of sound, in an ideal gas approximation. This is because pressure and density both contribute to the velocity of sound equally, and in an ideal gas, both effects cancel out each other leaving just the effect of temperature. Composition of air also has negligible effects on the speed of sound.
Therefore, the correct answer is Option (B).

Note
The minimum distance in which a sound wave repeats itself is called its wavelength. That is, it is the length of one complete wave. It is denoted by a Greek letter lambda. We know that in a sound wave, the combined length of a compression and an adjacent rarefaction is called its wavelength. Also, the distance between the centres of two consecutive compressions or two consecutive rarefactions is equal to its wavelengths.
We should know that the distance between the centres of a compression and an adjacent rarefaction is equal to half of its wavelength. The S.I unit for measuring wavelength is metre or m.