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Announcements 2/22/11

Announcements 2/22/11. Prayer Dispersion lab due tonight Labs 4 & 5 due Saturday I will have office hours today. Ripple Tank image: wikipedia. Interference. Path length Constructive Destructive Demo: Moire pattern transparencies Video: Two outdoor speakers. Reading Quiz.

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Announcements 2/22/11

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  1. Announcements 2/22/11 • Prayer • Dispersion lab due tonight • Labs 4 & 5 due Saturday • I will have office hours today

  2. Ripple Tank image: wikipedia Interference • Path length • Constructive • Destructive • Demo: Moire pattern transparencies • Video: Two outdoor speakers

  3. Reading Quiz • In a standing wave, the points that have the maximum vibration are called: • nodes • antinodes

  4. Standing Waves • Demo: Rubber tubing Image from Wikipedia

  5. Standing Waves • Will occur whenever you have two waves (same frequency, wavelength) moving in opposite directions • Math: A cos(kx - wt) + A cos(kx + wt)  From trig.: cos(a–b) + cos(a+b) = 2cos(a)cos(b) • Can occur via refletions of a single wave! But timing (frequency) has to be just right for it to occur over & over again • Web demo, revisited http://www.colorado.edu/physics/phet/simulations/stringwave/stringWave.swf Image by Colton

  6. Demos • Video: http://stokes.byu.edu/standing_script_flash.html • Demo: “Ladies belt” • Videos: Bowling ball, goblet, [Tacoma Narrows bridge] • Demo: Trumpet “Resonance”

  7. Standing Wave Patterns • Back to Ladies belt demo • What kinds of patterns do you get? • “node” vs “antinode” • Harmonics

  8. Standing waves on a string: “Closed-Closed” • For stable patterns: L = _______ • What are the frequencies? • Relative to the fundamental frequency? L =_____ L=_____ L =_____ L

  9. Standing waves in air: “Open-Open” Open end Open end • Quick writing: draw what you think the second harmonic should look like • For stable patterns: L = _______ • What are the frequencies? • Relative to the fundamental frequency? • Demo: Trumpet, again L=_____ Example: organ pipe

  10. Standing waves in air: “Open-Closed” Open end Closed end • Quick writing: draw what you think the second, third, and fourth harmonics should look like • For stable patterns: L = _______ • What are the frequencies? • Relative to the fundamental frequency? • Why wasn’t trumpet in this category? L=_____

  11. Standing Waves in 2D • Again, from Wikipedia Advertisement for Physics 318!

  12. Standing Waves in 3D • From Colton and Wienkes, Rev. Sci. Instr., 2009 • Light waves, frequency = 10 GHz (microwaves) Do they exist? Class poll Advertisement for Physics 641! 

  13. Final Demo • Flame standing waves

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