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Voiceover: Check out this ray of light.

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When it enters a new medium, like water,

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its path will bend, and the
larger the index of refraction

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of the new medium, the
more the light will bend

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from its initial direction
that it had in the air.

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This follows from Snell's Law,

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since if the index of
refraction is larger,

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the angle of the refracted
light must be smaller,

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and in order to have a smaller
angle from the normal line,

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the light ray has to bend more
from its initial direction.

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But here's the interesting thing,

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when you send in white light,

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composed of all visible wave lengths,

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the colors will disperse and
get separated from each other.

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We call this separation
of light, dispersion.

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So, why does dispersion happen?

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The reason for dispersion is
that the index of refraction

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for water and most other
materials are actually

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a function of the wavelength of the light.

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For instance, if you ask a physicist,

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or look up the index
of refraction of water,

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most sources would say the
index of refraction of water

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is 1.33, but what those
sources or physicists

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really mean is that
the index of refraction

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is pretty much 1.33 for
the entire visible range

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of wavelengths; however,
each visible wavelength

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has a slightly different
index of refraction in water.

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The index of refraction
of red light in water

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is about 1.33, but the index of refraction

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of blue light is closer to about 1.34.

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In fact, for most materials
the smaller the wavelength

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of the light, the larger
the index of refraction,

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which means smaller wavelength
light will bend more

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than larger wavelength light
will in most materials.

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This is why in water the violet
light would bend the most,

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since it has the smallest
wavelength for visible light.

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Blue light would bend slightly less,

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green light a little less,

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yellow light a little less than that,

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orange light even less,

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and red light would bend the least.

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So, remember, dispersion
and the rainbow patterns

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that emerge result from the fact that

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most materials have an index of refraction

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that's a function of the
wavelength of the light,

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and in most materials, the
smaller the wavelength,

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the more the light will bend.