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Chapter 12_solutions

# Chapter 12_solutions - Chapter 12 Sound Student 2 A sound...

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Chapter 12 Sound Student: ___________________________________________________________________________ 2. A sound wave radiates from a source in all directions. If the power of the sound source is 200 watts, then the intensity level of the sound wave 100 m from the source is, in dB: A. 98.5. B. 92.0. C. 91.5. D. 89.6. E. 88.3. Sound decibels (dB) are defined with respect to the “threshold of hearing” which corresponds to an intensity of I 0 =10 -12 W/m 2 . Moreover, each 10- fold increase in intensity increases the dB by 10. As a formula, this gives: 10 dB log 10 (I/I 0 ) In this problem, we first have to find the intensity I = P/(4 R 2 ) = (200 W)/(4 (100 m) 2 ) = 1.59 x 10 -3 W/m. Then we find 10 dB log (1.59x10 -3 /1x10 -12 ) = 92 dB. 25. The sound of a bird singing is given as 5 dB. What is the intensity of the sound of a bird singing? A. 1.95 10 -12 W/m 2 B. 2.04 10 -12 W/m 2 C. 2.98 10 -12 W/m 2 D. 3.16 10 -12 W/m 2 E. 4.25 10 -12 W/m 2 We use the same formula as in problem 2, but solve it for I: 10 dB log(I/I 0 ) = 5 dB. Then log(I/I 0 ) = 5/10 = 1/2 leading to I = I 0 * 10 1/2 = 1x10 -12 W/m 2 *3.16 = 3.16x10 -12 W/m 2 . 28. A 3.0 m organ pipe is open at both ends and contains air. The velocity of sound in air is 331 m/s. What is the wavelength of the lowest frequency mode?

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Chapter 12_solutions - Chapter 12 Sound Student 2 A sound...

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