1. INTERACTIONS OF WAVES Interference Refraction Diffraction
Doppler Effect
Polarization

2. 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

3. CONSTRUCTIVE INTERFERENCE
larger displacement (larger amplitude)
crest overlaps crest 
or tough overlaps trough

4. DESTRUCTIVE INTERFERENCE
smaller displacement (smaller amplitude)
crest overlaps trough 
displacement/ amplitude is reduced
crest cancels trough 

5. 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

6. 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

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

8. 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)

9. REFRACTION
What happens to the ray as it enters the water with less of an angle?

10. REFRACTION IN NATURE Wave speed depends on the medium
Click on picture for internet animation

11. 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 λ

12. DIFFRACTION Being able to hear around corners
Happens with light waves too (affects photography)

13. 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).

14. DOPPLER EFFECT
the shift in frequency of wave when a wave source and an observer are moving relative to each other
A stationary bug producing disturbances in water
A• • B
A bug moving to the right and producing disturbances
A• •B
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

15. DOPPLER EFFECT: SOUND Longer λ for observers as train leaves
Shorter λ for observers as train approaches

16. DOPPLER EFFECT: LIGHT
Longer λ for observers as train leaves = light shifts RED
Shorter λ for observers as train gets closer = Light shifts BLUE

17. 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

18. PRACTICE Reflection Refraction Diffraction Interference Polarization
Word bank:
Reflection
Refraction
Diffraction
Interference
Polarization
Doppler Effect

19. PRACTICE Reflection Refraction Diffraction Interference Polarization
Word bank:
Reflection
Refraction
Diffraction
Interference
Polarization
Doppler Effect

20. INTERFERENCE RESOURCES
for applets.
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)