The loudness of sound is determined by the
(A) amplitude of vibration
(B) ratio of amplitude and frequency of vibration
(C) frequency of vibration
(D) product of amplitude and frequency of vibration

Hint: Loudness is a sensation of how strong a sound wave is at a place. It is always a relative term. It is a dimensionless quantity. Its unit is decibel (dB). Factors affecting intensity are the amplitude of vibration. Density of the medium and the distance of source from the human ear.

Complete answer:
The amplitude of sound determines the loudness of sound. A sound that is faint will have a small amplitude while that of a loud sound will have larger amplitude.
The Intensity wave is defined as the power delivered per unit area. Intensity of the wave is proportional to the square of amplitude of the wave.
Amplitude of sound. The number of molecules displaced by a vibration creates the amplitude of a sound. The strength or level of sound pressure. The number of molecules in the sound wave in b is greater than the number in the sound wave in a, therefore the amplitude of the sound wave in b is greater.

So, the correct answer is “Option A”.

Note:
The energy in a sound wave can be measured using decibels. The Decibel meter shows examples of things that make noise and measurements in decibels. Amplitude measures in decibels of sound pressure. Usually, we are asking as if there is just “one” amplitude of sound waves in the air. The loudness perception of a sound is determined by the amplitude of the sound waves. The higher amplitude the louder the sound or the noise.