Question

The loudness of sound depends on:
A. Its amplitude
B. Its frequency
C. Its time period
D. Its speed

Answer 1

Hint: The loudness of sound is a function of its intensity and intensity in turn is determined by the strength of the wave or more particularly, its amplitude. As the intensity of the sound increases, the loudness of the sound is also said to increase. It does not have anything to do with the speed or time period.

Complete step by step answer:
The loudness of sound is dependent upon how intense the sound wave is or more particularly, the energy carried by it. This is dependent upon the strength of the wave. Usually for waves, this strength is a factor of the amplitude of the wave.
The amplitude of a wave is a measure of how high the crests and how low the troughs of the waves are. This wanes away as the sound travels in a medium since there is dissipation of the energy of the wave by the particles of the medium.
This is the reason why the loudness of sound is much more when you stand near a speaker but if you go one kilometer away, you may not hear anything at all. This is because the sound has to travel a distance in the medium and its amplitude becomes smaller and smaller due to dissipation of energy by the medium.
However, the frequency, speed and wavelength of the sound are constants in a medium and do not change regardless of the distance travelled by the wave in the medium. Hence, there is no dependency of the loudness of sound on these factors.
The larger the amplitude of the sound wave, the higher is the energy and intensity and greater is the loudness of sound.
Hence, the correct option is A) its amplitude.

Note: Students might think that the loudness depends on the frequency of the sound since in quantum mechanics, energy of a particle is characterized by its frequency. They may also think that since the energy of light depends upon its frequency, sound must also be the same, but they must remember that light exhibits both wave and particle properties, however sound is purely a wave and the energy of a wave depends upon its intensity and amplitude.