INTERACTIONS OF WAVES

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INTERACTIONS OF WAVES

• Interference
• Refraction
• Diffraction
• Doppler Effect
• Polarization

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Reflection

• When an object or wave hits a surface through
  which it cannot, pass it bounces back. This is
  called reflection.

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Law of Reflection

• This law states the angle of reflection is
  congruent to the angle of incidence.

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Reflection

• Waves bounce back at a boundary.
• The reflected wave is exactly like the incident
  wave.
• At a fixed boundary , the wave will reflect but
  it will turn upside down.

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Fixed boundary
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INTERFERENCE
when 2 or more waves meet while traveling in the
same medium (overlapping waves)

• the NET displacement (amplitude) is the sum of
  the amplitude of the waves
• Constructive or destructive interference
• Creates standing waves beats

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CONSTRUCTIVE INTERFERENCE
larger displacement (larger amplitude)
crest overlaps crest ?
or tough overlaps trough
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DESTRUCTIVE INTERFERENCE
smaller displacement (smaller amplitude)
crest overlaps trough ?
displacement/ amplitude is reduced
crest cancels trough ?
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BEATS INTERFERENCE
Overlapping waves of different f (frequencies)

• In music interference creates beats (changes in
  loudness softness)

• Wave 1 (red) and
• Wave 2 (blue)
• combine to form beat pattern (in green)High
  amplitude LOUD
• Low amplitude soft

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STANDING WAVES INTERFERENCE
when two overlapping waves traveling in opposite
direction have the same frequency

• Points that have no displacement ? NODES
• Large, moving displacements ? ANTINODES(max.
  amplitudes)
• String instruments

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CONSTRUCTIVE INTERFERENCE

• Resonance
• When an object vibration at a particular
  frequency
• Seen in musical instruments, especially strings
• Sympathetic resonanceWhen one vibrating object
  induces a vibration in another object
• Soldiers do not walk in formation across
  bridges
• Tacoma Narrows Bridge

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REFRACTION
when a wave changes direction ( speed) as it
passes from one medium into another

• Refraction depends upon density of medium
• Greater densities mean greater refraction (i.e.
  more bending)

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REFRACTION
What happens to the ray as it enters the water
with less of an angle?
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REFRACTION IN NATURE
Wave speed depends on the medium
Click on picture for internet animation
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DIFFRACTION
when a wave bends around an edge or spreads
through an opening

• familiar examples sound waves (speakers in a
  room) and water waves (breaker opening in
  harbors)
• the amount of diffraction increases with
  increasing ?

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DIFFRACTION

• Being able to hear around corners
• Happens with light waves too (affects photography)

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How is DIFFRACTION different from REFRACTION?

• Diffraction wave bends around an edge
• Refraction wave bends because it changes from 1
  medium to another (and, therefore, changes
  speed).

• http//www.acoustics.salford.ac.uk/feschools/waves
  /diffract.htm

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DOPPLER EFFECT
the shift in frequency of wave when a wave source
and an observer are moving relative to each other
Notice how waves near B are compressed ? ƒ
higher
Waves leaving A are expanded ? ƒ lower

• apparent increase in ƒ for observers as the
  source approaches/ moves closer to observer
• apparent decrease in ƒ for observers as the
  source recedes / moves away from observer

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DOPPLER EFFECT SOUND

• Longer ? for observers as train leaves
• Shorter ? for observers as train approaches

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DOPPLER EFFECT LIGHT

• Longer ? for observers as train leaves light
  shifts RED
• Shorter ? for observers as train gets closer
  Light shifts BLUE

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POLARIZATION
when the displacement of a transverse wave is in
a specific orientation or direction ? familiar
example polarized sunglasses
polarized materials only allow waves that
correspond to a special direction to pass through
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PRACTICE
Word bank Reflection Refraction Diffraction Inter
ference Polarization Doppler Effect
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PRACTICE
Word bank Reflection Refraction Diffraction Inter
ference Polarization Doppler Effect
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INTERFERENCE RESOURCES

• http//www.kettering.edu/drussell/Demos/superposi
  tion/superposition.html for applets.

• http//www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?
  t35 for applet.
• To change frequencies, etc., enter new value, and
  RETURN.
• To pause, left click.

• For Harmonics Beats applets link to The Soundry
  Sound Lab (left sidebar)http//library.thinkquest
  .org/19537/