Question

Phon is unit of:
A. Wavelength
B. Loudness
C. Frequency
D. Intensity

Answer 1

Hint: The sound wave is a longitudinal wave which is characterized by physical quantities like the frequency, the wavelength, the intensity of the sound etc. The intensity of the sound is calculated using the loudness of the sound.

Complete step by step solution:
Intensity of the sound is not the same as the loudness of the sound. So, saying that two sounds have equal intensity doesn’t mean that both the sound is having the same level of loudness.

The human hearing sensitivity varies with frequency of the sound. If 1000 Hz is chosen as a standard frequency, then each equal loudness curve can be marked as reference to the decibel level at 1000 Hz. This is the basis for the measurement of loudness in phons. If a given sound is perceived to be as loud as a 60 dB sound at 1000 Hz, then it is said to have a loudness of 60 phons.
It is important to realize that the phon is used only to describe sounds that are equally loud. It cannot be used to measure relationships between sounds of differing loudness. For instance, 40 phons is not twice as loud as 20 phons. In fact, an increase of 10 phons is sufficient to produce the impression that a SINE TON is twice as loud.
For the purpose of measuring sounds of different loudness, the SONE scale of subjective LOUDNESS was invented. One sone is arbitrarily taken to be 40 phons at any frequency, i.e. at any point along the 40 phon curve on the graph. Two sones are twice as loud, e.g. 40 + 10 phons = 50 phons. Four sones are twice as loud again, e.g. 50 + 10 phons = 60 phons. The relationship between phons and sones is shown in the chart, and is expressed by the equation:
Phon = \[40+10\text{ }lo{{g}_{2}}\](Sone)

Hence, phon is the unit of the loudness of the sound.

Note:- Decibel is the unit of intensity of the sound.
- Phon is the unit of the loudness of the sound.