Question

The velocity of sound in vacuum is:
A.) $0$
B.) $330\text{ }m\text{ }{{s}^{-1}}$
C.) $360\text{ }m\text{ }{{s}^{-1}}$
D.) $660\text{ }m\text{ }{{s}^{-1}}$

Answer 1

Hint: Sound is a mechanical wave which means that it requires a material medium to travel. In a medium sound travels by continuously stretching and compressing the particles of the medium that in turn do so to their neighboring particles and hence a wave like disturbance propagates through the medium. Presence of material particles in the medium is essential for the propagation of sound.

Complete step by step answer:
Sound waves are mechanical waves. Mechanical waves travel in a material medium by the help of disturbances produced by the material particles of the medium. A sound source creates a disturbance by stretching and compressing the particles of the medium near it, which in turn stretch and compress their neighboring particles. In this way, a wavelike disturbance is created in the medium which propagates through the medium by the constant stretching and compressing of the particles.

However, in the absence of a material medium, there are no particles which can stretch and compress and propagate the sound wave. Therefore, sound cannot travel in the absence of a material medium. Hence, sound cannot travel in vacuum.

Therefore, the speed of sound in vacuum is zero.

Hence, the correct option is A) $0$.

Note: Students often confuse the properties of the speed of light and sound. The speed of light in vacuum is not zero. In fact it is the highest theoretically obtainable speed in the universe. This is because light is an electromagnetic wave and does not depend on the presence of a medium for its propagation.
The explanation of propagation of sound is also the reason why sound travels fastest in solids, slower in liquids and slowest in gases. In solids, the particles are very close together and hence, the neighboring particles can be easily excited and energy can be carried forward. Hence, the speed of propagation of sound will also be greater. In liquids, the particles are further apart while in gases they are furthest and hence, the speed of sound is also less.