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14.3 W ave Interactions

14.3 W ave 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).

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14.3 W ave Interactions

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  1. 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)

  2. Reflection http://www.youtube.com/watch?v=23z0i2PpSzg http://www.youtube.com/watch?v=aVCqq5AkePI

  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 http://www.youtube.com/watch?v=BH0NfVUTWG4

  4. Refraction • Waves also bend when they go from one medium to another • That’s how eye glasses and magnifying glasses work (light) http://www.youtube.com/watch?v=KgqV975EtA0

  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 http://www.youtube.com/watch?v=ypcX1LdmMPM http://www.youtube.com/watch?v=IU8xeJlJ0mk

  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. • 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?

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