Question

The sound travels fastest in:
(a) Solids
(b) Liquids
(c) Gases
(d) None of these

Answer 1

Hint: The speed of the sound will be dependent on the density of the medium through which it will be traveling. We also know that the sound waves will be travelling by the method of longitudinal propagation. The density of solids, liquids and gases will be different. The density of the medium will be dependent on the molecules present in the medium.

Complete step-by-step solution:
The sound waves can travel through a medium by the method of longitudinal propagation. This means that there will be alternate contraction and expansion of the particles in the medium. The propagation of this kind of waves will be primarily dependent upon the density of the medium. If the propagation of the sound can be considered as the propagation of disturbance in the medium. When we discuss the case of solids, in solids, the density will be more if compared to that of gases. If the density is increased the collisions will be increased. Hence, the disturbance will be increased. Because of the closeness of the particles, the collisions take place very quickly. This will make the sound wave travel at a higher speed. Hence, the correct answer is option (a).

Note: The dependence of the speed of sound on the density of the medium in case of gases should be also discussed. This is because students usually try to use the formula of the speed of sound in gases for the case of solids too. So, the formula governing the speed of sound in gases would be:
$v=\sqrt{\dfrac{\gamma P}{\rho }}$
Here v will be the speed of sound γ will be the coefficient of adiabatic expansion, P is the pressure of the gas, and ρ is the density of the gas. The density will be inversely proportional to speed, unlike in the case of solids. The speed of light decreases with an increase in density in the case of gases.