College Physics (7th Edition)

Published by Pearson
ISBN 10: 0-32160-183-1
ISBN 13: 978-0-32160-183-4

Chapter 14 - Sound - Learning Path Questions and Exercises - Exercises - Page 525: 40

Answer

The threshold of pain for sound is usually taken to be around 140 dB, although this can vary somewhat depending on the individual. We can use the formula for calculating the combined intensity level of multiple sound sources to determine how many bands would need to play simultaneously to produce a sound level at or above the threshold of pain. The formula is: IL_total = 10 log(I_total / I_ref) where IL_total is the combined intensity level of the sound sources, I_total is the total intensity of the sound sources, and I_ref is the reference intensity (1 x 10^-12 W/m^2). We can rearrange this formula to solve for I_total: I_total = I_ref * 10^(IL_total / 10) If we want to find out how many bands would need to play simultaneously to produce a sound level of 140 dB, we can set IL_total = 140 dB and I_ref = 1 x 10^-12 W/m^2: I_total = (1 x 10^-12 W/m^2) * 10^(140 / 10) I_total = 1 W/m^2 Now we need to determine the intensity level produced by a single band. We are told that the intensity level for a single band is 110 dB. We can use the formula for converting between intensity and intensity level to find the intensity produced by a single band: IL = 10 log(I / I_ref) 110 dB = 10 log(I / (1 x 10^-12 W/m^2)) I = 1 x 10^-7 W/m^2 Now we can substitute this value for I into the formula for I_total: I_total = n * I where n is the number of bands playing simultaneously. We want to find the value of n that makes I_total at least 1 W/m^2: 1 W/m^2 = n * (1 x 10^-7 W/m^2) n = 1 x 10^7 Therefore, 10 million bands playing simultaneously would be needed to produce a sound level at or above the threshold of pain. However, it is important to note that this calculation assumes perfect mixing of the sound from all the bands, which is unlikely to occur in reality. In addition, exposure to sound at this level can cause permanent hearing damage, so it is important to wear appropriate hearing protection at concerts and other loud events.

Work Step by Step

The threshold of pain for sound is usually taken to be around 140 dB, although this can vary somewhat depending on the individual. We can use the formula for calculating the combined intensity level of multiple sound sources to determine how many bands would need to play simultaneously to produce a sound level at or above the threshold of pain. The formula is: IL_total = 10 log(I_total / I_ref) where IL_total is the combined intensity level of the sound sources, I_total is the total intensity of the sound sources, and I_ref is the reference intensity (1 x 10^-12 W/m^2). We can rearrange this formula to solve for I_total: I_total = I_ref * 10^(IL_total / 10) If we want to find out how many bands would need to play simultaneously to produce a sound level of 140 dB, we can set IL_total = 140 dB and I_ref = 1 x 10^-12 W/m^2: I_total = (1 x 10^-12 W/m^2) * 10^(140 / 10) I_total = 1 W/m^2 Now we need to determine the intensity level produced by a single band. We are told that the intensity level for a single band is 110 dB. We can use the formula for converting between intensity and intensity level to find the intensity produced by a single band: IL = 10 log(I / I_ref) 110 dB = 10 log(I / (1 x 10^-12 W/m^2)) I = 1 x 10^-7 W/m^2 Now we can substitute this value for I into the formula for I_total: I_total = n * I where n is the number of bands playing simultaneously. We want to find the value of n that makes I_total at least 1 W/m^2: 1 W/m^2 = n * (1 x 10^-7 W/m^2) n = 1 x 10^7 Therefore, 10 million bands playing simultaneously would be needed to produce a sound level at or above the threshold of pain. However, it is important to note that this calculation assumes perfect mixing of the sound from all the bands, which is unlikely to occur in reality. In addition, exposure to sound at this level can cause permanent hearing damage, so it is important to wear appropriate hearing protection at concerts and other loud events.
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