(a) Find the intensity 9.0 m from the source.
(b) Find the intensity level in decibels at that distance.
(c) At what distance would you experience the sound at the threshold of pain, 120 dB?
I found (A) to be correct at 0.098 W/m2
And I found (C) to be correct at 2.82 m....
I need help with (B)...I cant seem to get the correct answer!
(b) Find the intensity level in decibels at that distance.
(c) At what distance would you experience the sound at the threshold of pain, 120 dB?
I found (A) to be correct at 0.098 W/m2
And I found (C) to be correct at 2.82 m....
I need help with (B)...I cant seem to get the correct answer!
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Thanks for telling me it is chapter 14, that is very important.
The area of a sphere 9 meter in radius is 4πr² = 1018 m²
intensity = 100W /1018 m² = 0.098 W/m²
b) to convert to dB, you need to state a reference.
I'll use dB SIL (Sound Intensity Level), reference to 10^-12 W/m²
0.098 W/m² / 1e-12 W/m² = 0.098e12
dB = 10 log 0.098e12 = 109.8 dB
c) same as b in the reverse
ratio = 10^(120/10) = 1e12
comparing to the reference level, that is
ratio = 1e12 x 1e-12 = 1 W/m²
so at what distance is the sound 1 W/m²
100 W / 1 W/m² = 100 m², ie, where the area of the sphere is that
A = 4πr² = 100
r = 2.82 meters
The area of a sphere 9 meter in radius is 4πr² = 1018 m²
intensity = 100W /1018 m² = 0.098 W/m²
b) to convert to dB, you need to state a reference.
I'll use dB SIL (Sound Intensity Level), reference to 10^-12 W/m²
0.098 W/m² / 1e-12 W/m² = 0.098e12
dB = 10 log 0.098e12 = 109.8 dB
c) same as b in the reverse
ratio = 10^(120/10) = 1e12
comparing to the reference level, that is
ratio = 1e12 x 1e-12 = 1 W/m²
so at what distance is the sound 1 W/m²
100 W / 1 W/m² = 100 m², ie, where the area of the sphere is that
A = 4πr² = 100
r = 2.82 meters