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