Speed of sound

Why sound travels faster in humid air than normal air as humid air is denser than normal air? (Akash asked)


The speed of sound in a medium is inversely proportional to the square root of its density. Humid air is less dense than dry air. Therefore the speed of sounf in humid air is greater than that in dry air.


Are you thinking why dry air is more than that of humid air? This is a common misconception. Students used to think that humid air is denser than dry air. But it is not so. Just like skimmed milk (milk removed off its cream) is more dense than normal milk (with cream). Density of cream is much less than that of the rest of milk. So when it is removed, the residual milk becomes denser.

Humid air contains water vapor content. Water vapor is lighter than air. So when air contains water vapor, its density is less. When the water content is removed, it becomes denser.

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