set7-soln

set7-soln - Physics 1240 Homework 7 solutions Brief...

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Physics 1240 Homework 7 solutions Brief solutions to homework set #7. Your numbers will be diﬀerent, but the idea is the same. I’m just using sample numbers here. 1. Suppose a sound of frequency 1200 Hz is emitted from a speaker 15 meters away from you. At your location, the intensity is 10 - 6 W/m 2 . Let me assume your eardrum has area 3 × 10 - 5 m 2 . If the sound continues for 2 seconds, what total amount of energy is received by your ear? Do you suppose this level of energy deposit would be harmful to you? The key relation here is that total energy is intensity times area times time, or in equations E = IAt . Therefore E = IAt = (10 - 6 J/s/m 2 ) × (3 × 10 - 5 m 2 ) × (2 s) = 6 × 10 - 11 J . This intensity of sound is about 10 6 times the minimal audible intensity, so it has a SIL of 60 dB. This is well below the SILs associated with hearing loss, so I expect that receiving this amount of energy in my ears would not be harmful. 2. Your stereo is set to a sound intensity level (SIL) of 50 dB. I’d like to know what this means in terms of energy ﬂow: what is the intensity of the sound wave this produces? Note: When

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This note was uploaded on 08/24/2010 for the course PHYS 1240 taught by Professor Holland,murray during the Spring '08 term at Colorado.

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set7-soln - Physics 1240 Homework 7 solutions Brief...

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