Outline for 4/20: Announcements demos Interference of...
Transcript of Outline for 4/20: Announcements demos Interference of...
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Ch. 17: waves (sound)
Outline for 4/20:
• Announcements• Nature of sound• demos• Speed of sound• Interference of sound waves• HITT quiz
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Announcements
• Final exam Sat, April 28. Covers all material,slight emphasis on Chs. 13,15-17(10:00am to noon)
Rooms: Carlton 100: Aa-MaFlint Hall 50: Mc-PoMatherly 0018: Ra-RyWeil 270: Sa-Vo
McCarty B G086: Wa-Zz
Reviews: Hirschfeld/Korytov NPB1001 Apr 27 2nd-3rd periods Kahya NPB 2165 Apr 24 7pm-9pmBomstad NPB 1101 Apr 26 2nd-3rd periodsWhiting NPB 2205 Apr 25 7pm-Shankar NPB2205 Apr 26 7pm -
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Announcements cont’d
• Final WebAssign HW12 due Tues, Apr. 24 at 11pm.
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Sound
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Sound as pressure wave
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Speed of sound
HRW derives
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Relation between pressure wave and density wave
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Interference of 2 sound waves
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Problem 1
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Sound intensity
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Intensity scale - decibels
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HITT Quiz
A B
Fiendish IFAS scientists expose a helpless alligator to pure sine wave sound coming from two speakers each 5 m from the alligator.Speaker A emits wave which are 180 degrees out of phase with speakerB, each with source power 250 W. What intensity does the alligator hear, in W/m2? (Note: this is a “point alligator”).
A. 10/p B. 20/p C. 50/p D. 100/p E. 0
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HITT quiz soln
Ans: E. Since the sources are 180 degrees out of phase, thesound waves arriving at the alligator cancel. The alligatoris then at a node of the standing wave, and intensity is zero.