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Wave Interactionshttp://www.physicsclassroom.com/mmedia/
waves/ltm.cfm
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BoundaryWhere 2 media meetWhere wave conditions changeReflection, transmission, or both can occur
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Waves at BoundariesA wave travels from one medium to another
(i.e. air into water)- Waves enter the new medium upright- How much energy is transmitted into the new
medium depends on how different the media are.- The greater the difference in the media the less
transmission- More of the energy is reflected (returns to the
original medium)
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Waves at Boundaries
When the wave goes from low density to high density the reflected wave is flipped (In this case it would return on the bottom)
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Waves at Boundaries
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Free/Open/Loose BoundaryBoundary that can move
- Boundary moves in response to the wave- When wave travels from:
- More dense to less dense - Wave remains upright upon reflection
- Less dense to more dense- Wave flips upon reflection
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Fixed BoundaryBoundary that does not move
- Most energy is reflected- Wave flips upon reflection (crest becomes a
trough)
Boundary Conditions
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Free BoundaryBoundary that does move
- Most energy is reflected- Wave maintains orientation upon reflection
(crest stays a crest)
Boundary Conditions
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AbsorptionIn the real world - some of the energy is absorbed by the
medium in the form of heat (usually as a result of friction)
- Some of the wave amplitude is lost as a result
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InterferencePrinciple of Superposition -when the particles of a medium are affected by multiple waves at the same time
-the oscillation of each particle is the combination of the oscillation that would occur as a result of each individual wave
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Types of InterferenceConstructive Interference:When multiple waves add up to create a larger amplitude
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Types of InterferenceDestructive Interference:When multiple waves add up to create a
smaller amplitude
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InterferenceConstructive Interference
Destructive Interference
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Standing Wavesoccur when a wave is confined between two
boundariesWave is reflected back and forth
• As the frequency changes the standing wave pattern changes
• low frequency, long wavelength
• high frequency, short wavelength
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Standing WavesStanding Waves applet
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Standing WavesInterference occurs between the wave and its reflectionWhere destructive interference occurs, nodes form
Node – particle remains at equilibriumWhere maximum constructive interference occurs, antinodes form
Antinode – particle is farthest from equilibrium
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DiffractionBending of waves around a boundary- no change in medium
Huygen’s Principle- Each molecule that is part of a wave
front emits its own wave front- Individual wave fronts are circular- When many circular wave fronts
overlap only the combined affect is seen
- Very far from an individual source, the combined wave front appears straight
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DiffractionWhen a straight wave front hits a boundary
the edges of the individual wave fronts show
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DiffractionThe amount of bending that is noticeable depends on the wavelength and the size of the opening
Wavelength ≥ slit size → more bending
Wavelength < slit size → less bending
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Diffraction and Interference When there are multiple openings the diffracted waves will overlap and interfere
Constructive interference occurs when wave fronts are in phase
i.e. where crests happen at the same time and place (where lines overlap on the diagram)
Destructive interference occurs when wave fronts are out of phase
i.e. where a crest and a trough happen at the same time and place (where lines overlap spaces on the diagram)
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Diffraction and Interference Where constructive
interference occurs an increase in amplitude occurs (brighter area on diagram)Wave form is magnified
Where destructive interference occurs a decrease in amplitude occurs (grey areas on diagram)Wave form is cancelled out
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What Depends on WhatFrequency: depends on source
Amplitude: depends on energy
Speed: depends on medium