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PHYS16 – Lecture 34

PHYS16 – Lecture 34. Waves December 3, 2010. “Interference is much clearer in HD”. Outline for Oscillations. Simple Harmonic Motion Position, Velocity, Acceleration Force Energy Phase Damping Resonance Waves Mechanical waves Interference Standing waves. Mechanical Waves.

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PHYS16 – Lecture 34

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  1. PHYS16 – Lecture 34 Waves December 3, 2010 “Interference is much clearer in HD”

  2. Outline for Oscillations • Simple Harmonic Motion • Position, Velocity, Acceleration • Force • Energy • Phase • Damping • Resonance • Waves • Mechanical waves • Interference • Standing waves

  3. Mechanical Waves

  4. Mechanical Waves • A propagating oscillation that moves through a medium Transverse – water waves Longitudinal – sound waves

  5. Mechanical Waves • Waves use at least 1-3 space dimensions and time… • Ex. – Water waves propagate in x, move “up and down” in y, and change position with time • Ex. – Sound waves propagate in x, move “up and down” in x, and change position with time

  6. Wave Properties • Period – high period medium period low period T

  7. Wave Properties • Period – • Wavelength and Wave number – http://seagrant.uaf.edu/marine-ed/curriculum/images/stories/grade7/wave.jpg

  8. Wave Properties • Period – • Wavelength and Wave number – http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/Images_specific/wave_def.gif

  9. Wave Properties • Period – • Wavelength and Wave number – • Wave speed – http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/Images_specific/wave_def.gif

  10. Mechanical Wave – Position of Particle Plane Wave Higher Dimension Wave

  11. Ripple Tank Simulation

  12. Example Question 1 PhET website

  13. Example Question 2 PhET website

  14. Example Question 2 Speed = Period = Wave number = Wavelength = 330 m/s 0.0038 s 5.0m-1 1.25 m PhET website

  15. Example Question 3 • Sand is placed on the vibrating plate below. Which apparatus is vibrating the plate with the highest wave number?

  16. Wave on a String

  17. Wave on a String • You can generate a wave on a string by pulsing sting with your hand • Speed of pulse/wave is related to tension in string and mass density of string PhET website

  18. Propagation of Pulse • If you advance the movie one frame point A will move… (higher, lower, right, left)? • If generate new pulse but more quickly than first then it will be… (same, wider, narrower)? • If generate new pulse but move hand higher than first then it will be… (same, taller, shorter)? • If generate new pulse with rope tightened then pulse will be… (same, faster, slower)? PhET website

  19. Wave on String Simulation PhET website

  20. Example Question PhET website

  21. Superposition, Interference, and Standing Waves

  22. Superposition and Interference • Superposition - When two stimuli overlap they will superimpose, or the new stimulus will be the sum of the two individual stimuli • Interference – the superposition of two or more waves, amplitudes sum together • “out of phase” or phases shifted by 180 degrees then they will “destructively” interfere • “in phase” or phases not shifted then they will “constructively” interfere

  23. Interference Constructive Destructive PhET website

  24. Interference http://www.rp-photonics.com/img/interference2_s.png

  25. Standing Waves • Standing waves – waves that constructively interfere in cavity and “stand” in one spot Node Antinode http://kottan-labs.bgsu.edu/teaching/workshop2001/chapter7_files/image023.gif

  26. Example Question 1 PhET website

  27. PhET website

  28. PhET website

  29. Example Question 2 • A string of 0.25 kg/m is stretched to a tension of 4 N between 2 plates that are 0.5 m apart. What is the wavelength of the first harmonic in the string? • 4 m • 2 m • 1 m • 0.5 m • 0.25 m

  30. Main Points - Waves • Mechanical Wave – a propagating oscillation that moves through a medium • Superposition – wave amplitudes add together • Interference – when two or more waves superimpose (destructive -> less A and constructive -> bigger A) • Standing waves – waves that constructively interfere within a cavity and appear to “stand” in one spot

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