A trumpet creates a sound intensity level of 1.02 102 dB at a distance of 0.80 m
ID: 1297200 • Letter: A
Question
A trumpet creates a sound intensity level of 1.02 102 dB at a distance of 0.80 m. (a) What is the sound intensity of a trumpet at this distance? (b) What is the sound intensity of five trumpets at this distance? (c) Find the sound intensity of five trumpets at the location of the first row of an audience, 8.20 m away, assuming, for simplicity, the sound energy propagates uniformly in all directions. (d) Calculate the decibel level of the five trumpets in the first row. (e) If the trumpets are being played in an outdoor auditorium, how far away, in theory, can their combined sound be heard?
Explanation / Answer
beta = 102 dB
r = 0.80 m
a) beta = 10 log [I / 1 * 10-12]
102 = 10 log [I / 1 * 10-12]
I = 0.0158 W/m2
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I1 = 5 * 0.0158 = 0.079 W/m2
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I2 r22 = I1 r12
I2 = [0.079] * [0.82 / 8.22]
= 7.52 * 10-4 W/m2
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beta' = 10 log [I / 1 * 10-12]
beta' = 10 log [7.52 * 10-4 / 1 * 10-12]
beta'= 88.76 dB
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They have to travel to long distance from the eqn of part c to make I2 as zero
we cannot hear sound after 2 to 3 km because there is dossipiation of energy whilepropagating through air
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