14.3 W ave Interactions
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Transcript of 14.3 W ave Interactions
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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)
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Reflection
http://www.youtube.com/watch?v=23z0i2PpSzghttp://www.youtube.com/watch?v=aVCqq5AkePI
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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
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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
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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
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Interference
• Constructive interference
• Destructive interference
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• For light waves, it cancause different colors (e.g. bubbles, oil spills)
• For sound, it causes the vibrations to happen at same time (beats)
Interference
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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.
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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 manywavelengths of each are there to the left?
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