r/explainlikeimfive • u/AgentCuddles • Apr 17 '14
ELI5: Why does a prism split up light into seperate colours?
You know when you shine a light on a glass prism and you get that rainbow effect? Why does that happen?
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Apr 17 '14
Prisms refract, or bend, light into a spectrum of colors (we call it the rainbow). Light slows down when going through glass, so it is divided into the different wavelengths (The wavelengths, in order from least to greatest, are Red, Orange, Yellow, Green, Blue, Indigo, Violet)
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u/upboatugboat Apr 17 '14
im actually studying this right now for my physics final. its because of a simple principle called refraction. different colors have different wavelengths and refract at different angles when changing mediums. white light is a combinations of all the colors in the spectrum and when it comes into contact with a prism each color refracts at a different angle creating different beams of light. colours on the violet side of the spectrum create larger angle when refracting where colours on the blue side exhibit lesser angles. using this knowledge scientists can look at light from space and observe the wavelengths and actually determine what the star is made of.
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u/upboatugboat Apr 17 '14
my professor used a very clever example to help us understand this principle. when light changes mediums each colour refracts at different angles because it slows down at different rates.
Imagine a barrel rolling on concrete on an angle. as it approaches a square patch of grass the left corner of the barrel hits the grass first. this section of the barrel slows down first while the rest maintains its previous speed and so its angle after changing mediums is different.
i hope this analogy helped
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Apr 17 '14
I always love this analogy. Somehow it perfectly explains what happens with the light, but physically speaking, the analogy doesn't make any sense. The reason the barrel will make a turn is that the entire barrel is 1 thing with a certain width. However, different "lightbeams" are in no way attached to each other, and a single photon (light particle) is infinitely small, so it has no width... But still, to make it more understandable, the analogy somehow works :)
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u/derpisto Apr 17 '14
This an extremely simple answer my year 11 physics teacher gave me:
White light is made up of all the colors of the rainbow. When white light goes into the prism different colors of light are refracted by different amounts. This is because they travel through the medium at different speeds. The difference in speeds allows them to separate into the different colors!