Diffraction and interference of light | Physics | Khan Academy 

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Light spreads out when it encounters an obstacle. This process is called diffraction. Diffraction is most noticeable when the obstacle is similar in size to the wavelength of the light. When light waves diffract around obstacles, they overlap each other. This overlap results in constructive and destructive interference at different locations, producing an interference pattern.
Sections:
00:00 - Intro
00:49 - Coin in front of a flashlight
01:23 - Hair in front of a laser
02:27 - Diffraction of water waves
06:14 - Effect of wavelength and obstacle size
08:25 - Diffraction of laser light around hair
09:37 - Why Hubble images have spikes
11:17 - Interference of diffracted waves
Image credits:
"Hubble views the dawn of a Sun-like star" by NASA/ESA, CC BY 2.0
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"Monkey Head Nebula" by NASA/ESA, CC BY 2.0
www.flickr.com/photos/nasahub...
Laguna Superior (16.367952, -94.852309) by Google Maps
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