Question

What is the loudness of sound measured in?
(a). Decibels
(b). Meters
(c). Kilograms
(d). Seconds

Answer 1

- Hint: Loudness of sound is the interpretation by the amplitude per unit area in at a point in space, which is intensity. The unit of intensity is the unit loudness will be measured in.

Complete step-by-step solution -
Consider you are listening to music on a speaker, if the amplitude is low, you go near the speaker to listen to the music. Whereas, for the music to be audible at a distance, we will then increase its amplitude. The amplitude depends on the energy with which sound has been created. It is all about energy. Imagine a point source of sound, as the speed of sound is uniform, the sound reaches the surface of a sphere with radius R at the same time. So, essentially the energy it transmitted has spread all along the sphere. The energy per unit area is defined as intensity.
Loudness refers to how loud or soft a sound seems to a listener. The loudness of sound is determined by the intensity of the sound waves. Intensity is a measure of the amount of energy in sound waves.
The unit of intensity is the decibel (dB). Decibels are measured on a logarithmic scale with the base 10. The equation for loudness looks similar to:
$\text{Loudness = 10lo}{{\text{g}}_{10}}\left( \dfrac{I}{{{I}_{0}}} \right)dB$ Where, Io is a constant.
That is for every 10 dB increase in the intensity of sound, loudness is 10 times greater.
Therefore, the answer to this question is option A. Decibels.

Note: Other options can be eliminated if you put a thought into ‘can they really measure loudness? If so, then how?’ Meter is the unit of length; kilogram is used to measure mass and second is used to measure time.