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old homework 35 - ramos(dar2447 oldhomework 35 Turner(58120...

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ramos (dar2447) – oldhomework 35 – Turner – (58120) 1 This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 3) 10.0 points An electric guitar’s amplifier is at a distance of 5.3 m. Find the intensity of its sound waves when its power output is 0.31 W. Correct answer: 0 . 000878213 W / m 2 . Explanation: Let : r = 5 . 3 m and P = 0 . 31 W . I = P 4 π r 2 = 0 . 31 W 4 π (5 . 3 m) 2 = 0 . 000878213 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 0.61 W. Correct answer: 0 . 0017281 W / m 2 . Explanation: Let : P = 0 . 61 W . I = 0 . 61 W 4 π (5 . 3 m) 2 = 0 . 0017281 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 2.8 W. Correct answer: 0 . 00793225 W / m 2 . Explanation: Let : P = 2 . 8 W . I = 2 . 8 W 4 π (5 . 3 m) 2 = 0 . 0017281 W / m 2 . 004 (part 1 of 2) 10.0 points The area of a typical eardrum is about 4 . 7 × 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: 4 . 7 × 10 17 W. Explanation: Let : A = 4 . 7 × 10 5 m 2 and I 0 = 1 × 10 12 W / m 2 . At the threshold of hearing, I = P A P = I A = ( 1 × 10 12 W / m 2 ) ( 4 . 7 × 10 5 m 2 ) = 4 . 7 × 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: 4 . 7 × 10 5 W. Explanation: Let : I = 1 W / m 2 . At the threshold of pain, P = ( 1 W / m 2 ) ( 4 . 7 × 10 5 m 2 ) = 4 . 7 × 10 5 W . 006 10.0 points Two sound sources 3 m apart have the same frequency of 870 Hz. The sources emit energy in the form of spherical waves. An observer initially hears a minimum sound, since the sound sources are out of phase, at a distance 22 m along the perpendicular bisector of the line joining the two sources. What distance x must the observer move along a line parallel to the line joining the two sources before hearing another sound of
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ramos (dar2447) – oldhomework 35 – Turner – (58120) 2 minimum intensity? The speed of sound is 354 m / s. Correct answer: 3 . 0186 m. Explanation: Let : d = 3 m , y = 22 m , f = 870 Hz , and v = 354 m / s . At the beginning, the path difference between the two sources for the observer is 0 but the phase difference is π , since he heard the sound of minimum volume, which means that an original phase difference exists between the two sources.
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