14.3 Wave Interactions Reflection – Waves bounce back when they meet a surface or boundary – 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)

Reflection

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 G4 G4

Refraction Waves also bend when they go from one medium to another That’s how eye glasses and magnifying glasses work (light) ch?v=KgqV975EtA0 ch?v=KgqV975EtA0

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 –

Interference Constructive interference Destructive 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 ) Interference

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. 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.

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?