How Light Wave Interference Works

When white light hits a film of oil floating on water, most of it passes through the film, but some of the light is reflected off the top and bottom layers of the film. Check out this HowStuffWorks podcast to learn more about light wave interference.

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Episode Transcript

Speaker 1 (00:00):
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(00:21):
happens him Marshall brain. It's very common to see rainbow
patterns when you look at the surface of a c
D and also when you look at soap bubbles or
a thin film of oil floating on still water. Where
do these colors come from? All three of these rainbow
effects are created when light waves interact with each other.

(00:45):
It's known as constructive and destructive interference of the light
hitting thin surfaces. Think about a very thin film of
oil floating on water as an example. When white light
hits the film, most of it passes through the film,
but some is reflected off the top and bottom layers
of the film. In the same way. When you stand

(01:07):
in front of a window in your house, you can
see a reflected image in the window. Most of the
light is passing through the window and out of the house,
but some is reflected back at you. The light that
reflects off the top layer of a film of oil
travels slightly shorter distances than the light reflecting off the
bottom layer. If the film is very thin on the

(01:30):
order of the wavelength of light, then interference can occur.
Violet light has a wavelength of about four thousand angstroms,
and angstrom is a hundred millions of a centimeter, while
red light has a wavelength of about seven thousand, six
hundred angstroms, so we are talking about extremely thinned films.
If the film is just the right thickness, a red

(01:53):
light wave a side wave will bounce off the top
and bottom layers in perfect alignment, and the tubers a
sign ways will combine to double the amount of red
light scene, or they may reflect exactly out of phase
and the red light will be eliminated. Because specific colors
can be doubled or eliminated depending on the thickness of

(02:14):
the film, it changes the color of light and we
see colors like colors of the rainbow coming off the film.
On a CD, the surface is mirrored, so the rainbow
colors are much more intense. In a c D, the
angle that the CD is held at controls the colors
you see. The angle, along with the bumps on the

(02:36):
c D surface, controls the path difference and therefore the
colors you see. Do you have any ideas or suggestions
for this podcast? If so, please send me an email
at podcast at how stuff works dot com. For more
on this and thousands of other topics, go to how
stuff works dot com. Brain Stuff is sponsored by Harry's

(02:58):
dot com. Get a great evening experience for a fraction
of the price. The quality of the shave is so
important that Harry's purchased the factory that makes their blades.
Fifteen dollars gets you a set that includes a handle,
three blades, and shave cream. Go to Harry's dot com.
Use the code brain stuff to save five dollars off
your first purchase.