1. Wave Interactions

2. Boundary Where 2 media meet Where wave conditions change
Reflection, transmission, or both can occur

3. Waves at Boundaries
A 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)

4. 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)

6. Waves at Boundaries

7. Free/Open/Loose Boundary
Boundary 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

8. Fixed Boundary Boundary that does not move Most energy is reflected
Wave flips upon reflection (crest becomes a trough)
Boundary Conditions

9. Free Boundary Boundary that does move Most energy is reflected
Wave maintains orientation upon reflection (crest stays a crest)
Boundary Conditions

10. Absorption In 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

11. Interference
Principle 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

12. Types of Interference
Constructive Interference: When multiple waves add up to create a larger amplitude

13. Types of Interference
Destructive Interference: When multiple waves add up to create a smaller amplitude

14. Interference
Constructive Interference Destructive Interference

15. Standing Waves occur when a wave is confined between two boundaries
Wave is reflected back and forth
As the frequency changes the standing wave pattern changes
low frequency, long wavelength
high frequency, short wavelength

16. Standing Waves
Standing Waves applet

17. Standing Waves Interference occurs between the wave and its reflection
Where destructive interference occurs, nodes form
Node – particle remains at equilibrium
Where maximum constructive interference occurs, antinodes form
Antinode – particle is farthest from equilibrium

18. Diffraction Bending 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

19. Diffraction
When a straight wave front hits a boundary the edges of the individual wave fronts show

20. Diffraction
The 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

21. 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)

22. 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

23. What Depends on What Frequency: depends on source
Amplitude: depends on energy
Speed: depends on medium