11.3 - Optical Phenomena in Nature

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The sun must be behind you to see a
rainbow, and it must reflect off of water
droplets in the air
The colours you see are due to a combination
of reflection, refraction, and dispersion
through these water droplets
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A rainbow forms when light enters a water droplet
and refracts, reflects off the inner surface of the
droplet, and then refracts again when leaving the
droplet, causing dispersion
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Sundogs appear as bright spots on both sides
of the sun
They appear when ice crystals in the
atmosphere refract sunlight (as opposed to
water droplets for rainbows)
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An image can be formed by either reflection
of light (as in a mirror) or refraction of light
You can use ray diagrams to show where the
refracted image is located
Apparent depth is an optical effect in which
the image of an object appears closer than
the object itself
◦ Often occurs when you are looking from the air into
water
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Light rays from the object travel to your eyes, but the rays
have refracted at the surface of the water
The image of the box is located by tracing the refracted rays
backwards until they meet (just like for reflection!)
Notice that the box on the bottom of the pool looks like it is
higher than it actually is – in reality, the bottom of the pool is
deeper than it appears to be
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Shimmering and mirages are caused by
refraction of light in unevenly heated air
When light travels through air at different
temperatures, it refracts because hot air is
less dense than cold air
Because there is no distinct boundary
between sections of air at different
temperatures, the light does not bend at one
specific point – it travels along a curved path
Also, since air is usually moving, the direction
and the amount of bending are constantly
changing
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You can see this in the air above any hot
surface – the objects look wavy
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Occurs on a much larger scale than
shimmering
Most commonly seen in very hot deserts or
on highways – the sand or paved surface
becomes extremely hot after being in
sunlight for several hours
The hot ground heats the air just above it,
making the lower layer of air much hotter
than the higher air
When sunlight reaches the hot air near the
ground, the sunlight is refracted upwards
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An object that appears to be on the ground but is not
really there is called a mirage
The solid, curved line below shows the path of light
from the sky; the dashed line shows how your brain
interprets the scene
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