Question

Let the speed of sound in air, water and iron by ${V_a},{V_w},{V_i}$ respectively. Which is the correct order of decreasing velocity of sound in these media?
A) ${V_i} > {V_a} > {V_w}$
B) ${V_w} > {V_i} > {V_a}$
C) ${V_a} > {V_w} > {V_i}$
D) ${V_i} > {V_w} > {V_a}$

Answer 1

Recall that the sound is defined as the vibrations that travel in a medium. These vibrations are produced when the particles of the medium collide with each other. These vibrations produce a disturbance which is called sound. This disturbance travels in the form of a longitudinal wave.

Complete step by step solution:
The particles in solids are very closely packed and the space between them is very small. Also the solids are denser. So the disturbance passes from one particle to another in a very short time. But the liquids have some space between its particles. They are less dense than solids but more denser than gases. So the disturbance will take more time to pass than in solids.
Whereas the particles in gases are loosely packed and have very large spaces between them. They are less dense than the solids and liquids. So the disturbance will take most time to pass in gases. They will produce sound after solids and liquids. This is because the velocity of sound will be maximum in solids and minimum in gases.
It is clear from above discussion that the velocity of sound will be maximum in iron since it is a solid. The air is a gas so the velocity of sound will be minimum in air.
$\therefore$The order of the velocity of the sound will be
${V_i} > {V_w} > {V_a}$

Option D is the right answer.

Note: It is to be noted that the sound waves have regions of high pressure and low pressure also known as compressions and rarefactions, which move at a particular speed. Also sound can travel in any medium but it can not travel in vacuum. That is why there is no sound in outer space.