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Tip the CD and see how that changes
the reflections. Change the distance from the CD to the paper. What happens
to the colors?
Take a close look at your CD. It's made of aluminum
coated with plastic. The colors that you see on the CD are created by white
light reflecting from ridges in the metal.
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When light reflects off or passes through something with many
small ridges or scratches, you often get rainbow colors and interesting
patterns. These are called interference patterns. Here are several other
ways you can see interference patterns.
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Squint at a distant bright light at night. You'll see starburst patterns
around the light. If you look closely, you can see colors in the patterns.
These patterns form when light bends around your eyelashes and imperfections
in the layers that make up the lens of your eye. Tilt your head to one
side while watching the pattern and notice that the pattern moves with
you.
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In a dark room, look at a bright light (maybe a candle flame) through
a nylon stocking, a silk scarf, a feather, or a tea strainer. The pattern
that you see depends on what you look through. Move the thing you're looking
through and notice that the pattern moves with it.
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Buy a set of "rainbow glasses" in a toy store or a science
shop. Through these glasses, all lights look like rainbows. The glasses
are made with diffraction gratings, clear plastic that is etched with many
lines.
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Why does a CD reflect rainbow colors?
Like water drops in falling rain, the CD separates white
light into all the colors that make it up. The colors you see reflecting
from a CD are interference colors, like the shifting colors you see on a
soap bubble or an oil slick.
You can think of light as as being made up of waves-like
the waves in the ocean. When light waves reflect off the ridges on your
CD, they overlap and interfere with each other. Sometimes the waves add
together, making certain colors brighter, and sometimes they cancel each
other, taking certain colors away.
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Published by Owl Books,
Henry Holt & Company, New York,
1996 & 1997
ISBN 0-B050-4536
&
ISBN
0-8050-4537-6
,
$12.95 each
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© 1998
Exploratorium
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Take the CD out of its case and take a look at
the blank side (the side that doesn't have any printing on it). You'll see
bands of shimmering color. Tilt the CD back and forth and the colors will
shift and change.
Hold the CD in the sunshine. Or if it's a cloudy
day, turn out the lights and shine your flashlight at the CD. Hold your
piece of white paper so that the light reflecting off the CD shines onto
the paper. The reflected light will make fabulous rainbow colors on your
paper.
