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HW15-solutions

# HW15-solutions - kuehner(rjk679 HW15 Mackie(20211 This...

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kuehner (rjk679) – HW15 – Mackie – (20211) 1 This print-out should have 7 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Sound level β in decibels is defined as β 10 log parenleftbigg I I 0 parenrightbigg , where I 0 = 1 × 10 12 W / m 2 . The decibel scale intensity for busy traffic is 80 dB. Two people having a loud conversation have a deci- bel intensity of 70 dB. What is the approximate combined sound intensity? Correct answer: 0 . 00011 W / m 2 . Explanation: Let : β 1 = 80 dB , β 2 = 70 dB , and I 0 = 1 × 10 12 W / m 2 . I = I 0 10 β/ 10 , so the combined sound intensity I is I = I 1 + I 2 = I 0 parenleftBig 10 β 1 / 10 + 10 β 2 / 10 parenrightBig = (1 × 10 12 W / m 2 ) ( 10 8 + 10 7 ) = 0 . 00011 W / m 2 . 002 (part 1 of 2) 10.0 points Two sound sources radiating in phase at a fre- quency of 560 Hz interfere such that maxima are heard at angles of 0 and 20 from a line perpendicular to that joining the two sources. The velocity of sound is 340 m/s. y L d S 1 S 2 θ listening direction θ δ Assume: L d Find the separation between the two sources. Correct answer: 1 . 77517 m. Explanation: Let : f = 560 Hz , v = 340 m / s , θ 1 = 0 , and θ 2 = 20 . r 2 r 1 y L d S 1 S 2 θ = tan 1 parenleftBig y L parenrightBig listening direction δ d sin θ r 2 r 1 P O negationslash

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HW15-solutions - kuehner(rjk679 HW15 Mackie(20211 This...

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