CD Spectroscope
Materials:
Procedure:
1.
Take
the CD that you have and hold it in your hand by the edges. Look carefully at
the side that doesn't have any writing
on it, this is the side with all of the encoded information. Tilt the CD back
and forth in the light that is in the room. Do
you see any rainbows?
2.
While
holding the CD with the information/rainbow side up, wrap the long card stock
around the CD. What you are trying to do is to make a little container like an
open coffee can with the card stock as the sides and the CD as the bottom. The
notch cut into the card stock should be at the bottom. You are going to use
this notch to view the information/rainbow side of the CD.
3.
Tape
the card stock into the form of a tube that it is now in. Also fasten the CD to
the card stock tube with two pieces of tape. Make sure that you are putting the
tape on the writing side only. If you put tape on the information side, you may
damage the CD.
4.
Take
your square piece of card stock and place this square directly onto the top of
your open tube and CD container. The only thing to be careful of is to make
sure that the slit is directly over the notch in the tube. Tape the top onto
the tube.
You now have
a finished CD spectroscope. The way to use it is to hold a light source up to
the slit on the top, and look inside the container through the notch. You
should see a very clear strip of rainbow color running from the center hole of
the CD to the notch. Move the light source around to see what angle gives the
best spectrum.
Try other
sources of light. Different light has different color strengths. If you have
trouble seeing the spectrum of some specific light, try going into a dark room
and having the light you are testing being the only light.
A spectroscope does this by using a diffraction grating, which is an optical device consisting of an assembly of narrow slits or grooves, which by diffracting light produces a large number of beams which can interfere in such a way as to produce spectra.
The information side of a CD provides us with a manufactured diffraction grating. The surface of a CD has many small pits in the plastic, arranged within concentric rings; that surface has a thin layer of metal applied to make the pits more visible. By shining light onto the information side of a CD we create a pattern of interference on the grating that separates the beam of light into a number of spectra depending on the length of the waves in the beam.
Diffraction gratings are also present in nature. For example, the iridescent colors of peacock feathers, mother-of-pearl, butterfly wings, and some other insects are caused by very fine regular structures that diffract light, splitting it into its component colors.
