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Announcements 10/14/11

Dive into the concepts of standing waves, interference, and wave reflection. Discover the nodes and antinodes in a standing wave pattern, explore harmonic frequencies, and observe resonance patterns with engaging demos and videos. Get ready to understand the physics behind standing wave phenomena!

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Announcements 10/14/11

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  1. Announcements 10/14/11 • Prayer • Lab 3 ends Saturday • See email for some more info about the “uncertainty principle” used in the lab

  2. Ripple Tank image: wikipedia Interference • Path length • Constructive • Destructive • Video: Two outdoor speakers (1:16)

  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 (1:48) • Demo: “Ladies belt” • Videos: Bowling ball (0:50), goblet (1:42) • Youtube (on your own time): 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 and third harmonics 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! 

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