Question

Define the term intensity of a sound wave. State the unit in which it is measured.

Answer 1

Hint: The intensity of a sound wave is the energy characteristic of the sound. The intensity of a sound wave can be varied and is independent of the frequency.

Complete step by step answer:
The amount of energy flowing per unit time through per unit area perpendicular to the direction of propagation of the wave is called the intensity of the sound wave. For a sound wave, amplitude of the wave is related to the intensity, and so loudness depends on the intensity of the sound.
For example, consider sound waves from a speaker travelling to a person’s ears. When the volume is turned down, the loudness of the sound also decreases. This is because the energy carried by the sound waves is decreased and so intensity is reduced. Again on turning the volume up, the energy carried by the sound waves is increased, so intensity increases, and in turn the loudness of the sound increases.
Also, sound intensity decreases with distance. If two people whisper a conversation, the sound waves produced are of low intensity and not heard at a far distance. However, when a person shouts, it is heard at a far distance. The sound waves made by the person’s shouts have high intensity and so can be heard farther away.
 The intensity of sound wave is expressed in $$\text{J/}{\text{m}}^2\text{s}$$or $$\text{W/}{\text{m}}^2$$.

Note:
Two sounds of the same intensity, that is, equal energy per unit time per unit area, but different frequencies may not appear to be equally loud even to the same listener because the sensitivity of the ear is different for different frequencies.