Wave InteractionsWave InteractionsChapter 20 Section 3
Objectives:Objectives:Describe reflection, refraction,
diffraction, and interference
Compare destructive interference with constructive interference
Describe resonance, and give examples
Reflection:Reflection:When a wave bounces back after hitting
a barrier
All waves can be reflected (water, sound, light…)
Light: light waves from the sun are reflected when they strike the surface of the moon
Sound: reflected sound waves are an echo
Reflection:Reflection:
http://realastrologers.com/wp-content/uploads/2008/08/full-moon-reflection-350-px.jpg
http://www.fettes.com/academic/Physics%20at%20Fettes%20College/images/GraphicRippleTank11.jpg
Refraction:Refraction:The bending of a wave as the wave
passes from one medium to another at an angle
When a wave enters a new medium, the wave changes wavelength & speed
Result: the wave bends and travels in a new direction
Refraction:Refraction:
http://www.schoolforchampions.com/science/images/waveobstacle-refraction.gif
Refraction of Different Refraction of Different Colors:Colors:Colors in sunlight are refracted by
different amounts
The light is dispersed (spread out) into its separate colors
Why? Light waves travel through empty space at the same speed. Passing through other media (water, glass) the speed of the light wave depends on the wavelength of the light wave
Refraction of Different Refraction of Different Colors:Colors:
http://upload.wikimedia.org/wikipedia/commons/e/e9/Refraction_varies_by_frequency.gif
Diffraction:Diffraction:Most of the time, waves travel in
straight lines (ex: flashlight beam)
Sometimes waves bend or curve when they reach the edge of an object
Bending waves around a barrier or through an opening is known as: diffraction
Diffraction:Diffraction:If you can hear it, why can’t you see
it?
The amount of diffraction depends on the wavelength and the size of the barrier or opening the wave encounters
Sound wavelengths are long, light wavelengths are shorter
Diffraction (of water):Diffraction (of water):
http://www.gcsescience.com/Diffraction-Water-Waves.gif
Interference:Interference:All matter has volume, therefore
objects cannot be in the same place at the same time
Waves are energy, not matter, therefore waves can occupy the same space
The result of 2 or more waves overlapping is called: interference
Interference:Interference:Constructive Interference:
◦The crests of one wave overlap the crests of another wave or waves; waves combine
◦Energy combines
◦New wave has higher crests & deeper troughs (larger amplitude)
◦Waves approach, overlap, continue on….
Constructive Interference:Constructive Interference:
http://astro-canada.ca/_en/_illustrations/a4313_interferencecon_en_g.jpg
Interference:Interference:Destructive Interference:
◦When the crests of one wave and the troughs of another overlap
◦New wave has a smaller amplitude
◦If the original waves have the same amplitude, the result is no wave at all
Destructive Interference:Destructive Interference:
http://astro-canada.ca/_en/_illustrations/a4313_interference_en_g.jpg
Standing Waves: Standing Waves: A pattern of vibration that
stimulates a wave that is standing still
Certain parts of the wave are always at the rest position (destructive int.)
Other parts have a large amplitude (constructive int.)
Standing Wave:Standing Wave:
http://www.chem.umass.edu/genchem/whelan/class_images/111_Standing_Wave_Animated.gif
Resonance:Resonance:The frequencies at which standing
waves are made: resonant frequencies
When an object vibrating at or near the resonant frequency of a 2nd object causes the 2nd object to vibrate resonance occurs
Resonating objects absorb energy from the vibrating object
Ex: your voice sounds louder in the shower
Resonance:Resonance:
The Tacoma Narrows Bridge Collapse (1940)◦http://www.5min.com/Video/The-Orig
inal-Tacoma-Narrows-Bridge-Collapse-of-1940-119995718
◦http://www.youtube.com/watch?v=P0Fi1VcbpAI