Lecture_28_PPT

Lecture_28_PPT - Chapter 17 Sound Waves Categories of Sound...

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Chapter 17 Sound Waves
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Categories of Sound Waves z Audible waves are within the sensitivity of the human ear. Range is approximately 20 Hz to 20 kHz Audible sound
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Infrasonic waves z have frequencies below the audible range (<20 Hz) z Whales, elephants, hippopotamuses, crocodiles, birds and giraffes are known to use infrasound to communicate over distances. z Naturally from tornado, surf, earthquakes, volcanoes, waterfalls, calving of icebergs, aurora, lightning.
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Ultrasonic waves z have frequencies above the audible range (<20 kHz) z Bats (100kHz), Dogs, Dolphins and whales z Applications Ultrasonic Imaging Ultrasonic cleaning SONAR - navigation and ranging
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Periodic Sound Waves z A longitudinal wave is propagating through a gas- filled tube z The source of the wave is an oscillating piston z The distance between two successive compressions (or rarefactions) is the wavelength
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Periodic Sound Waves z As the regions travel through the tube, any small element of the medium moves with simple harmonic motion parallel to the direction of the wave z The harmonic position function is s (x, t) = s max cos (kx – ω t)
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Periodic Sound Waves z s (x, t) = s max cos (kx – ω t) z The variation in gas pressure, P = -B ds/dx = B k s max sin (kx- ω t) z B = v 2 ρ , ω =k v z P = ρ v ω s max sin (kx – ω t) = P max sin (kx – ω t) z P max = ρ v ω s max
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Periodic Sound Waves z s (x, t) = s max cos (kx – ω t) z P = P max sin (kx – ω t) z A sound wave may be considered either a displacement wave or a pressure wave
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Periodic Sound Waves z P = P max sin (kx – ω t) z s (x, t) = s max cos (kx – ω t) z The pressure is a maximum when the displacement is zero, etc.
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This note was uploaded on 01/28/2011 for the course PHYS 011 taught by Professor Nianlin during the Fall '08 term at HKUST.

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Lecture_28_PPT - Chapter 17 Sound Waves Categories of Sound...

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