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Assign15

# Assign15 - PHY 53 Summer 2010 Assignment 15 1 Take the...

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Assignment 15 1. Take the usual reference intensity for the db scale for sound, I 0 = 10 12 W/m 2 . a. What is the intensity of a sound of loudness 120 db? b. If this is the intensity of the sound at a rock concert at distance 90 m from the source, what is the average sound power output of the source? 2. Two waves of equal wavelength and frequency interfere. Separately the intensities of the two are I 1 and I 2 . a. Show that the maximum and minimum possible intensities for the combine, wave are I max = I 1 + I 2 ( ) 2 and I min = I 1 I 2 ( ) 2 . b. Specify one possible phase difference between the waves in each of these two cases. 3. Questions about standing waves. a. Write wave functions for two waves which, when superposed, will produce a standing wave of amplitude 0.02 m, speed 10 m/s, and with nodes 0.1 m apart. b. For sound waves in a pipe, an open end is a pressure node, like a fixed end on a string. Explain why. c. If you pluck a guitar string exactly in the middle you get only the odd numbered harmonics. Explain. 4. Three successive harmonics of an organ pipe have frequencies 850, 1190 and 1530 Hz. a. Is the pipe open at both ends or closed at one end? b. What is the fundamental frequency?

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