Question

A point source of sound radiates energy at the rate of 3.14 Watts Find the intensity level of loudness at a distance of 15.8 m from the source in dB (approximately)?

(take $\pi =3.14$)

• A. 9
• B. 12
• C. 16
• D. 18

Answer 1

The correct option is A 9

Consider a spherical surface of radius$=15.8m$ with the source at the center
$\therefore Intensity=\frac{Watt-power}{Area}$
$\therefore Intensity=\frac{3.14}{4\pi r^2}=\frac{3.14}{4\times 3.14\times {15.8}^2}W/㎡$
$\therefore$Intensity (in dB)$=\log \left[\frac{IntensityinW/㎡}{{10}^{-12}}\right]$
$\simeq 9dB$
Thus option A