Table 15.3 Intensity and sound intensity levels of common environmental sounds S
ID: 1778625 • Letter: T
Question
Table 15.3 Intensity and sound intensity levels of common environmental sounds Sound (dB) 1 (W/I Threshold of hearing Person breathing 1.0× 10-12 10 1.0×10-11 at 3 m A whisper, at I m Classroom during 1.0× 10-10 1.0×10-9 1.0×10-8 20 30 test, no talking Residential street, no traffic Quiet restaurant Normal conversation, 40 50 1.0×10-7 60 1.0×10-6 at I m Busy traffic Vacuum cleaner, 70 1.0×10-5 801.0×10-4 90 1.0×10-3 for user Niagara Falls, at viewpoint Pneumatic hammer at 2 m 100 0.010 Home stereo at max volume Rock concert Threshold of 110 0.10 120 1.0 pain 130 0 Part A Table 15.3 in the textbook gives an estimate for the sound intensity of a whsper at 1.0 m. What is the sound intensity of a whisper at a distance of 3.0 m. in Wm Express your answer using two significant figures. W/m Submit My Answers Give Up Incorrect; Try Again; 5 attempts remaining Part B What the corresponding sound intensity level in dB? Express your answer using two significant figures. dB Submit My Answers Give UpExplanation / Answer
a) Intensity of whisper at 1 m = I = 1*10^-10 W/m^2
Then Power = P = I*A = 1*10^-10*4pi*1^2 = 4pi*10^-10 W
Then intensity at distance 3m = I’ = P/(4pi*r’^2) = 4pi*10^-10/(4pi*9) = 1.1*10^-11 W/m^2
b) Intensity level in db = 10 log (I’/Io), where Io is the threshold intensity level (1 x 10^-12)
so, I’ = 10 log ( (1.1x10^-11) / (1x10^-12) ) = 10.4 dB
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