Chapter 11: Waves

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Chapter 11 Waves
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Types of Waves

• Wave disturbance that carries energy through
  matter or space.
• Example Stone dropped in waterwater particles
  dont moveenergy does.
• Mechanical waves those that travel through a
  mediummost waves
• Nonmechanical waves no medium
  necessaryelectromagnetic waves

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Waves Transfer Energy

• Waves carry energy
• they do work.
• Examples
• Water waves
• Sound waves
• Light waves
• Tsunami

Leaf, boat, shoreline, etc.
Eardrum
Eye or photographic film
Damage to coastal towns or shorelines
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Energy Spreads

• As a wave travels, the energy spreads.
• Larger the circlesmore the energy is spread.
• Example
• Stereo speakers.

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Vibrations Waves

• Vibrations involve energy transformations.
• Gravitational P.E.
• Elastic P.E.
• Kinetic E.
• Waves can pass though a series of vibrating
  objectsmasses on springs or particles in a
  medium.

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Transverse vs. Longitudinal

• Transverse waves perpendicular motion
• Examples light waves, S waves
• Longitudinal waves parallel motion
• Example sound waves, P waves

Animation
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Longitudinal Wave
Transverse Wave
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Surface Waves

• Boundary between 2 different mediums.
• Example Ocean waveswhat are the mediums?
• AIR and WATER

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Characteristics of Waves

• Transverse wave resembles a sine curve.
• Crest high points
• Trough low points
• Amplitude half the height between the crest
  trough/ determines amount of energy
• Larger amplitudelarger the amount of energy.

Animation
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• Longitudinal wave
• Compressions crowded areas / higher air
  pressure
• Rarefractions stretched-out areas / lower
  pressure

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• Wavelength distance between any two successive
  identical parts of a wave.
• SI Units Meter
• Symbol lambda (?)
• Wave train number of full waves in succession.
• How many wave trains?

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Crest
Wavelength
Displacement
Amplitude
Trough
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• Period how long it takes for waves to pass by.
• SI unit second
• Symbol T
• Frequency measure the rate of vibrations
• SI unit hertz (Hz)
• Symbol f
• Example If a sound is 20 000 Hz?20 000
  compressions are hitting your ear every second!

Animation
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Electromagnetic Spectrum

• The electromagnetic spectrum has a wide range of
  frequencies and wavelengths.

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Frequency-Period Equation

• Frequency of waves
• period
• f 1
• T
• Example If 2 waves pass by a buoy in 4 s, what
  is the frequency?
• f 1 2 0.5 Hz
• T 4 s

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Wave Speed

• How fast a wave moves? Depends on medium.
• Kinetic theory? Moves fastest in solids.
• Equations
• Speed wavelength or ? ?
• period T
• Wave speed frequency x wavelength
• or ? f ?

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Wave Speed Example

• The note for middle C has a frequency of 264 Hz.
  If the sound waves produced by the note have a
  wavelength of 1.3 m, what is the speed of the
  sound in the air?
• Frequency 264 Hz wavelength (?) 1.3 m
• f ? 264 Hz (1.3 m)
• 343 m/s Remember Hz 1/s

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Speed of Light

• Has finite speed.
• Speed of Light (c) 3 x 108 m/s (in a vacuum)
• All electromagnetic waves move at that speed.
• Slows down in a medium (air, water, etc.)

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Doppler Effect

• Pitch determined by frequency.
• Higher pitch?Higher frequency
• Lower pitch?Lower frequency
• Doppler effect change in the frequency of a
  wave due to motion of source or observer.
• Example Moving ambulance, train, etc.

Police Car Animation
Train Animation
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Wave Interactions

• Reflection bouncing back of a wave due to
  meeting a surface.
• Free boundaryreflected wave same as original.
• Fixed boundaryreflected wave opposite of
  original.

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• Diffraction bending of waves around an edge.
• Passing through an openingwaves bend around both
  edges.
• Another example?
• Doorway

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Diffraction of water waves (obstacle)
Diffraction of water waves (corner)
Diffraction of water waves (opening)
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• Refraction bending of waves due to passing
  through one medium to another.
• You see light coming from two different
  directions.
• Examples Spoon water.

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Interference

• A new wave that is different from the original
  waves.
• Resulting wave is found by adding the height of
  the wave at each point.
• Crest considered positive.
• Trough considered negative.
• Waves return to original form after interference.

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Constructive Interference

• Crests overlap troughs overlap.
• Resulting wave is the sum of both waves.
• Larger wave.
• Amplitudes are added.

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Destructive Interference

• Crest trough overlap.
• Resulting wave is the subtraction of both waves.
• Smaller wave.
• Amplitudes are subtracted.
• If crests troughs are the samethey cancel each
  other out.

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• Interference of light waves produces colorful
  displays.
• Oil slicks Butterfly wings Bird feathers
• Bubbles Liquid crystal Iridescence
• Interference of sound waves produces beats.
• Compressionslouder sound
• Rarefractionssofter sound
• Series of loud and softcalled beats

Animation
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Standing Waves

• Reflected waves that have the same amplitude,
  frequency, and speed as the original waves.
• Nodes points of no vibration.
• Antinodes points of maximum vibration.
• Can have only certain wavelengthsmultiple
  of half-wavelengths.

Animation 1
Animation 2
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References

• Wave Background Pic http//redhare.com/miscimgs/
  digital/planet_wave.jpg
• Speaker Pic http//www.vinyl-online.co.uk/assets
  /images/stereo_speaker_6.jpg
• Tsunami Pic http//www.personal.ceu.hu/departs/
  personal/Gabor_Toka/Pictures/Hokusai20In20the20
  Hollow20of20a20Wave20off20the20Coast20at20
  Kanagawa20(Views20of20Mt20Fuji20No.201).jpg
  
• Transverse/Longitudinal Wave Tuning Fork Pics
  Bug Doppler Pics http//sol.sci.uop.edu/jfalwar
  d/physics17/chapter10/chapter10.html
• Longitudinal Pulse Animation http//www.physicsc
  lassroom.com/mmedia/waves/lw.html
• Spring Pic http//online.cctt.org/physicslab/con
  tent/phyapb/lessonnotes/springs/oscillatingspring.
  gif
• Long. Transverse Surface Wave Animations
  http//www.gmi.edu/drussell/Demos/waves/wavemotio
  n.html
• Wave Pic http//id.mind.net/zona/mstm/physics/w
  aves/partsOfAWave/waveParts.htm
• Doppler Effect Graphic http//www.stmary.ws/phys
  ics/home/review/wave_test_2_tips.htm
• SineWave 1 http//www.jwgraphics.com.au/Technolog
  y/Maths_Function/sinewave.gif
• Sine Wave 2 http//home.alltel.net/okrebs/Ch8-10
  .gif
• Electromagnetic Spectrum http//www.nasa.gov/cent
  ers/langley/images/content/114284main_EM_Spectrum5
  00.jpg
• Diffraction Pic http//www.astro.queensu.ca/han
  es/p014/Notes/Figures/One_Hole_Diffraction.gif
• Oil Slick Pic http//www.ngsir.netfirms.com/engl
  ishhtm/Interference.htm
• Pencil Sound Refraction Pic
  http//hyperphysics.phy-astr.gsu.edu/hbase/geoopt/
  optpic/brokpen.jpg
• Constructive, Destructive, Bubble Pics
  http//www.olympusmicro.com/primer/lightandcolor/i
  nterference.html
• Meat Beetle Interference PicL
  http//fizyka.phys.put.poznan.pl/pieransk/Physics
  20Around20Us/Physics20around20us.html
• Peacock Feather Pic http//www.peacock.no/images
  /hjem_11.jpg
• Moth Pic http//www.butterfly-conservation.org/s
  pecies/b/peacock/photo_2.jpg