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## Question 9: Why sound waves move faster in solids than in gases?

ANSWER

Sound waves are mechanical waves and they need a medium for their propagation. So the effect of the nature of the medium is obvious.
The speed of sound is given by the equation

Where ‘E’ is the elasticity (Young’s modulus in case of solids and Bulk modulus in case of gases.) and ρ is the density of the medium.

If we consider the density aspects of solids and gases, the densities of solids is, no doubt, greater than gases.This means that unit volume of solids have more masses than gases. The density is in the denominator of the expression for the speed of sound. Thus it reduces the speed of sound in solids.
The elasticity of solids is far greater than the elasticity of the gases. This means solids easily restore its size and shape within the limit of elasticity.E is in the numerator in the expression for the speed of sound. Therefore, it increases the speed of sound in solids.
So, the speed of sound depends on the ratio of E and ρ of the medium. This ratio is always high in solid substances than gaseous. Therefore, speed of sound is also greater in solids than gases.

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