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Waves

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					            • Disturbances
            • All waves carry energy
            • Waves displace matter
               – Waves do NOT carry matter




http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
               Medium
• Medium – the material a wave travels
  through
   –When sound travels through air,
    the air is the medium
   –When sound travels through a
    solid, such as glass, the glass is the
    medium
Types of
 Waves
          Transverse Waves
• Examples: water waves, light waves, waves in a
  string or a rope, secondary seismic waves
• Displace the medium perpendicular to the
  direction the wave travels




      http://www.physicsclassroom.com/Class/waves/U10L1c.html
Crest
        Wavelength
                     amplitude




          Trough
          Longitudinal Waves
         (compression waves)
• Example: sound waves, primary seismic
  waves
• Displace the medium parallel to the
  direction the wave is moving




    http://www.physicsclassroom.com/Class/waves/U10L1c.html
    http://www.physicsclassroom.com/Class/waves/U10L2a.html



• http://members.aol.com/nicholashl/waves
  /movingwaves.html
                   (Wave animation)
      amplitude     compression




wavelength
                  rarefaction
    Wave
Interactions
              Reflection
• A wave “bounces
  back” when it
  encounters a new
  medium
• Law of reflection:
  the angle of
  reflection equals
  the angle of
  incidence
                            Reflection
                                             Reflection from a
                                             fixed boundary



                                             Reflection from
                                             a soft boundary

http://www.kettering.edu/~drussell/Demos/reflect/reflect.html
       Some Uses of Reflection
•   Mirrors
•   Communications
•   Radar
•   Sonar
                        Refraction
• A wave changes speed and direction
  (bends) when it enters a new medium
                                 Waves travel at different
                                 speeds in different mediums
                                 (due to density differences)
                                 When a wave strikes the
                                 boundary between mediums at
                                 an angle, one part of the wave
                                 slows down before another,
                                 and the wave bends
 Refraction animation - http://users.wpi.edu/~hkim/physics/refraction.swf
           http://www.williamson-labs.com/optical-body.htm


Light reflected from fish is bent as it travels
from water into the air.
To the viewer, it appears as if the fish is
along a straight line (the refracted ray)
Diffraction
      • A wave bends as it
        passes around a
        barrier
      • Used in
        spectroscopy
        (learning about the
        universe from the
        colors of light
        emitted from
        objects)
            Interference
• Two or more waves combine
  – Because waves are not matter (they are
    disturbances that displace matter), more than
    one wave can occupy the same space at the
    same time
  – This is called superposition
     Interference (continued)
• When two crests meet, their amplitudes
  are added (constructive interference)
• When a crest and a trough meet, their
  amplitudes cancel each other out
  (destructive interference)
• The resulting wave is the sum of the
  amplitudes at all points
Constructive and Destructive
       Interference
Superposition of Waves
Constructive and Destructive
       Interference

				
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posted:3/15/2012
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