Refraction and Rainbows

Refraction and Rainbows
Some of the most beautiful phenomena on Earth are simply
the result of bending light. A clear blue sky, rainbows, and the
reddish blaze of a setting sun are all the result of tricks of
light. Specifically, the colors produced in these light shows
are caused by refraction. Refraction is the bending of a wave
as it passes from one medium to another. Imagine pushing a
shopping cart from a smooth tile floor onto a grass lawn. As
the first wheel enters the grass and slows down while the
other wheels continue moving at the faster speed, the cart
changes direction. This is refraction. A wave bends in a
different direction when it enters a new medium because part
of the wave slows down while the rest of it continues at the
same speed. When light waves bend, colors can be produced.
Visible light is part of the electromagnetic spectrum. It travels
in waves just like sound, ultraviolet light, and x-rays do.
When a lamp is turned on or the sun is shining, the light from
these sources appears white. There are no specific colors that
can be seen in sunlight because the colors are all combined
into one. When the colors of light are
combined, they produce white light.
In 1665, famed physicist Isaac Newton
attempted to separate the colors of visible
light. He began by shining a light through
a prism. A prism is a solid structure with
two identical ends and all flat sides. Prisms
used in light experiments are made of
transparent materials such as glass or
plastic. When white light shined through
A prism separates white light into its
Newton’s prism, it separated into the
component colors. Many objects, such
individual colors of the visible spectrum.
as DVD surfaces, crystals, and
This is called dispersion. The colors are
diamonds, can act like prisms.
often nicknamed ROY G. BIV, which
stands for the first letter of each color: red, orange, yellow,
green, blue, indigo, and violet. Newton’s experiments led to
the understanding that white light is made up of colors that
refract at different angles when they pass through a medium
like a prism. This knowledge opened the door to explanations
of many of the colorful phenomena that occur in nature.
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Refraction and Rainbows
One of the best natural prisms is water. When white light
passes through raindrops, the light refracts, and the result is
one of the most colorful sights in nature: a rainbow. Sunlight
moves from the air into a water droplet at a particular angle.
The angle for each color of the rainbow differs because the
colors travel at different wavelengths. Red light has the
longest wavelength, while blue light has the shortest. When
red light enters a raindrop, it refracts the least because it
moves the fastest. However, blue light undergoes more
extreme refraction since it has such a short wavelength. Once
light enters a raindrop, it slows down and refracts. The light
is then reflected (or bounced off) the back inner surface of the
raindrop. It then passes back out of the front of the raindrop
and into the air. This causes the light to bend again as it exits
from its water medium to the air. Each raindrop refracts
white light differently depending on the angles. So each drop
emits a different color of the rainbow. One raindrop might
appear yellow, while another might
look green. Refracted light from
many raindrops is what forms the
colorful stripes of the rainbow.
The colors of the sky are also caused
by refraction. For centuries,
scientists tried to determine why the
sky was blue. It took many years to
solve, but the answer, they
discovered, lies in refraction. When
white sunlight reaches Earth’s
atmosphere, it is scattered in
A setting sun can set the sky ablaze with color as
the red end of the visible light spectrum is
different directions. The particles in
scattered.
the atmosphere cause this scattering.
Because blue light has the shortest wavelength, it is refracted
and scattered more than any of the other colors. This is why
the sky appears blue. The bluest part of the sky is the highest
point overhead, whereas closer to Earth’s surface, the color
fades to a pale blue or even back to white. This is because
light passes through a lot of the atmosphere in the low sky. It
is scattered so much by the molecules in the air and by
bouncing off the surface of Earth, that the light nearly all
recombines back into white light again.
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Refraction and Rainbows
Blue light scattering leads to some of the most beautiful
sunsets. Since the blue light is so scattered, the reds, oranges,
and yellows of the setting sun can more easily shine through
to our eyes. Also particles of pollution found in the lower
atmosphere, unfortunate as they are, more easily scatter light
at the red end of the spectrum. Smog, as it has been said, is
the reason that there are such beautiful sunsets.
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