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WAVES

WAVES. Background. Leonardo da Vinci – “ waves move but water does not; so waves transfer E (energy) without transferring matter” momentum (m x v) transfers E through matter in a manner similar to the way E transfers from one sphere to another in Newton’s Cradle. Newton’s Cradle.

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WAVES

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  1. WAVES

  2. Background • Leonardo da Vinci – “ waves move but water does not; so waves transfer E (energy) without transferring matter” • momentum (m x v) transfers E through matter in a manner similar to the way E transfers from one sphere to another in Newton’s Cradle

  3. Newton’s Cradle • Energy is transferred

  4. Basic Terminology • pulse = a single disturbance of E, energy transmittingfrom one place to another (ie: slinky) • traveling wave= generated when a pulse moves E along (ie) a slinky • wave = a series of pulses carrying E from one placeto another

  5. Three Types of Waves • 1. Mechanical waves – require matter & governed by Newton’s Laws (ie: water, sound, slinky spring); two types of mechanical waves to be discussed soon • 2. Electromagnetic waves – no medium required; travel at the speed of light (3.00 E 8 m/s) (ie: light, radio, x-rays, microwaves, infrared) e-m spectrum • 3. Matter waves– described by quantum mechanics (later – chapter 27) (ie: e-‘s and other sm. particles)

  6. Mechanical Wave Types • There are two types of Mechanical Waves: • Transverse • and • Longitudinal

  7. Transverse Waves • A type of Mechanical Wave • particles vibrate at right angles to the direction of the wave’s velocity • ie: Piano and guitar strings; surface water http://surendranath.tripod.com/Applets/Waves/Twave01/Twave01Applet.html

  8. Longitudinal Wave • Another type of mechanical wave • particles move parallel to the direction of the wave (sound, liquids) Compression Rarefaction http://surendranath.tripod.com/Applets/Waves/Lwave01/Lwave01Applet.html

  9. Click for Animations and additional info!

  10. Parts of a Wave Crest “Normal” or equilibrium line Amplitude Trough Wavelength

  11. NOVA | Electromagnetic Spectrum Tour

  12. Standing Waves • all musical instruments have standing waves • Nodes (destructive) and antinodes (constructive) are visible • Imagine a standing wave as waves traveling in opposite directions, as they would if trapped in a tube (as in microwave ovens) • node: undisturbed; medium is not displaced • antinode: the point of greatest displacement don’t appear to be traveling

  13. Standing Waves Antinode Node Applet!

  14. Formulas • v = l / T • f = 1 / T • v = lf

  15. Factors Affecting Wave Speed • does not depend on the amplitude or frequency of the wave, only on the properties of the medium

  16. Law of Reflection • “The angle of incidence = the angle of reflection” (assuming the same medium) • Incident wave – inbound wave • Reflected wave – outbound wave

  17. When Waves Travel Through Different Mediums

  18. When Waves Travel Through Different Mediums

  19. When Waves Travel Through Different Mediums

  20. When Waves Strike a Barrier • refraction: when a wave strikes a boundary, some E is reflected and some is transmitted or absorbed • diffraction: spreading of waves around the edge of a barrier (see graphic) • natural frequency: frequency at which a standing wave is produced (ie: glass breaking upon singing; car vibrates at certain speed; kidney stones blasted with sound) http://www.physics2000.com/Movies/Dog_View.mov • fundamental frequency – • lowest frequency – 1st harmonic • first overtone or 2nd harmonic • second overtone or 3rd harmonic http://maxwell.ucdavis.edu/~cole/phy9a/tacoma_narrows.mov

  21. When Waves Meet • Principle of Superposition – the displacement of a medium caused by 2 or more waves is the algebraic sum of the displacement caused by the individual waves • in phase: refers to the fact that the 2 combining crests and troughs are aligned; (if out of phase = they are not aligned) • Superposition of Waves (this is a link!) • interference: when 2 waves pass thru the same region of space at the same time, can be either…

  22. Constructive or Destructive Interference Constructive Destructive DESTRUCTIVE

  23. Total Destructive Interference From: www.lcse.umn.edu/.../ images/tot_con_inter.gif Practical Applications: Sound-Canceling Headphones

  24. Total Constructive Interference From: www.lcse.umn.edu/.../ images/tot_con_inter.gif

  25. Types of Interference

  26. How Waves Relate to Sound • Sound travels in waves • DECIBELS*when waves are sound waves, the amplitude is measured in decibels (dB)

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