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Unformatted text preview: hernandez (ejh742) – oldhomework 35 – Turner – (58120) 1 This printout should have 15 questions. Multiplechoice 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 5.1 m. Find the intensity of its sound waves when its power output is 0.23 W. Correct answer: 0 . 000703684 W / m 2 . Explanation: Let : r = 5 . 1 m and P = 0 . 23 W . I = P 4 π r 2 = . 23 W 4 π (5 . 1 m) 2 = . 000703684 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 0.59 W. Correct answer: 0 . 0018051 W / m 2 . Explanation: Let : P = 0 . 59 W . I = . 59 W 4 π (5 . 1 m) 2 = . 0018051 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 2.1 W. Correct answer: 0 . 00642494 W / m 2 . Explanation: Let : P = 2 . 1 W . I = 2 . 1 W 4 π (5 . 1 m) 2 = . 0018051 W / m 2 . 004 (part 1 of 2) 10.0 points The area of a typical eardrum is about 5 . 1 × 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 . 1 × 10 − 17 W. Explanation: Let : A = 5 . 1 × 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 . 1 × 10 − 5 m 2 ) = 5 . 1 × 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 . 1 × 10 − 5 W. Explanation: Let : I = 1 W / m 2 . At the threshold of pain, P = ( 1 W / m 2 )( 5 . 1 × 10 − 5 m 2 ) = 5 . 1 × 10 − 5 W . 006 10.0 points Two sound sources 2 m apart have the same frequency of 820 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 29 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 hernandez (ejh742) – oldhomework 35 – Turner – (58120) 2 minimum intensity? The speed of sound is 354 m / s....
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 Spring '08
 Turner
 Physics, Work, Wavelength, Correct Answer, Standing wave

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