Dispersion

~separating white light into the spectrum This can be done with refraction. Light bends when it enters a new medium. Each color bends a little bit differently. red bends the least, violet bends the most. If you use an appropriately shaped piece of glass, plastic or other transparent material you can separate the colors.

Diagram of a prism White light The triangle shape maximizes the separation. A complete picture looks like this

Rainbows Raindrops can also disperse light Sunlight Raindrop It reflects back here If we zoom way out of this diagram…

Rainbows Our raindrop is here Sunlight comes in At this height you only see red, all other colors pass over your head. But there are lots of raindrops You only see green here Cleaning this image up some.

Rainbows You only see green here You only see red here You only see violet here The other colors are in between. All other colors either pass over you or under you.

Total internal reflection This is not actually reflection, it is refraction. ~bending of light when it changes mediums This bending can cause the light to never leave the medium. So it appears to reflect instead of refract. This is called total internal reflection. Critical angle- minimum angle of incidence required for TIR to occur.

Diagrams of total internal reflection (TIR) Regular refraction TIR at critical angle TIR

Where you see total internal reflection (TIR) Diamonds They are cut so light can not get out except for the top facets You get flashes of light (sparkles) from certain facets It also disperses giving you several colors

Diamonds White light come in This is greater than the critical angle (24.6 o from the normal for a diamond) It will continually TIR and disperse until it hits the top (the only place that gives it a chance to get out)

Fiber Optics “light pipes” TIR light across a fiber. -like shooting a bullet through a pipe. fibers are made of a plastic or bendable glass. Fiber optic tubes can be used to illuminate hard to reach places. like for noninvasive surgery

Fiber optic tubes light comes in here and leaves here

Carrying information Fiber optic fibers carry light impulses just like wires carry electrical impulses. Except thin fiber optic fibers can carry more information than thick copper wires. Also fiber optic fibers don’t corrode very useful in undersea cables

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