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Unformatted text preview: zhou (cz3574) – HW14 – mackie – (10611) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. NOTE SAT DEADLINE 001 (part 1 of 3) 10.0 points An electric guitar’s amplifier is at a distance of 4.4 m. Find the intensity of its sound waves when its power output is 0.33 W. Correct answer: 0 . 00135643 W / m 2 . Explanation: Let : r = 4 . 4 m and P = 0 . 33 W . I = P 4 π r 2 = . 33 W 4 π (4 . 4 m) 2 = . 00135643 W / m 2 . 002 (part 2 of 3) 10.0 points Find the intensity of the sound waves when the amplifier’s power output is 0.52 W. Correct answer: 0 . 00213741 W / m 2 . Explanation: Let : P = 0 . 52 W . I = . 52 W 4 π (4 . 4 m) 2 = . 00213741 W / m 2 . 003 (part 3 of 3) 10.0 points Find the intensity of the sound waves when the amplifier’s power output is 3.3 W. Correct answer: 0 . 0135643 W / m 2 . Explanation: Let : P = 3 . 3 W . I = 3 . 3 W 4 π (4 . 4 m) 2 = . 00213741 W / m 2 . 004 (part 1 of 2) 10.0 points The area of a typical eardrum is about 5 . 3 × 10 − 5 m 2 . Find the sound power (the energy per sec- ond) incident on an eardrum at the threshold of hearing ( 1 × 10 − 12 W / m 2 ) . Correct answer: 5 . 3 × 10 − 17 W. Explanation: Let : A = 5 . 3 × 10 − 5 m 2 and I = 1 × 10 − 12 W / m 2 . At the threshold of hearing, I = P A P = I A = ( 1 × 10 − 12 W / m 2 )( 5 . 3 × 10 − 5 m 2 ) = 5 . 3 × 10 − 17 W . 005 (part 2 of 2) 10.0 points Find the sound power incident on an eardrum at the threshold of pain ( 1 W / m 2 ) . Correct answer: 5 . 3 × 10 − 5 W. Explanation: Let : I = 1 W / m 2 . At the threshold of pain, P = ( 1 W / m 2 )( 5 . 3 × 10 − 5 m 2 ) = 5 . 3 × 10 − 5 W . 006 10.0 points Sound level β in decibels is defined as β ≡ 10 log parenleftbigg I I parenrightbigg , where I = 1 × 10 − 12 W / m 2 . The decibel scale intensity for busy traffic is 81 dB. Two people having a loud conversation have a deci- bel intensity of 70 dB. zhou (cz3574) – HW14 – mackie – (10611) 2 What is the approximate combined sound intensity? Correct answer: 0 . 000135893 W / m 2 . Explanation: Let : β 1 = 81 dB , β 2 = 70 dB , and I = 1 × 10 − 12 W / m 2 . I = I 10 β/ 10 , so the combined sound intensity I is I = I 1 + I 2 = I parenleftBig 10 β 1 / 10 + 10 β 2 / 10 parenrightBig = (1 × 10 − 12 W / m 2 ) ( 10 8 . 1 + 10 7 ) = . 000135893 W / m 2 ....
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This note was uploaded on 03/25/2011 for the course PHYS 122 taught by Professor Hiyishi during the Spring '10 term at Temple College.

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Hw14 - zhou(cz3574 – HW14 – mackie –(10611 1 This print-out should have 18 questions Multiple-choice questions may continue on the next

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