1. 14.3 Wave Interactions Reflection
Waves bounce back when they meet a surface or boundary
(movie: reflection)
At a boundary free to move, the wave reflects in same shape.
At a boundary that doesn’t move (fixed), the wave is inverted.
This is what happens for mirrors (light) and echoes (sound)

2. Reflection

3. Diffraction
When waves pass the edge of a boundary, new waves are made.
This makes it look like the waves bend around the boundary.
why we can hear things we can’t see

4. Refraction Waves also bend when they go from one medium to another
(movie: refraction)
That’s how eye glasses and magnifying glasses work (light)

5. Interference Waves combine to make a new wave
Draw them on top of each other to see new wave
Constructive interference
Crest/troughs or compressions/rarefactions line up
Amplitude increases
Destructive interference
Crest/troughs or compressions/rarefactions don’t line up
Amplitude decreases, or can completely cancel out.
(movie: comparing const/destr interference)

6. Interference
Constructive interference
Destructive interference

7. Interference
For light waves, it can cause different colors (e.g. bubbles, oil spills)
For sound, it causes the vibrations to happen at same time (beats)

8. Standing Waves
The wave vibrates so that it looks like it’s standing still or flip- flopping back and forth.
Really waves are reflecting back and traveling in both directions at once.
(movie: standing waves)
Places where there are no vibrations (movement) are called nodes. Here there is perfect destructive interference, the waves have cancelled each other out.
Places of maximum vibration are called antinodes. Here there is perfect constructive interference and the waves have added together.

9. Standing Waves
This can only happen at certain wavelengths, related to the length of the medium.
More about this in
the next unit on sound
How many wavelengths of each are there to the left?