PHYSICS LAB SPECTROSCOPE

Lab 15 Spectroscopy

Make Your Own Spectroscope

Materials

· One empty cereal box

· Compact Disc

· Utility Knife (or scissors) – Be careful!

Procedure

1. Cut a 1" horizontal slit on the side of the cereal box just below the nutrition information.

2. Cut a slit across the opposite side of the box and extend it 1" on either side at an angle 45 degrees above the horizontal. (You want to insert the CD and have it angled. See the graphic below.)

3. Slide a CD into this slit.

4. Make an eyehole on the bottom of the box below the CD.

Here’s how it works.

A CD has the very cool property of behaving like a reflective diffraction grating. An ordinary diffraction grating is a grid of tiny, evenly spaced opaque lines on an otherwise transparent material. Light can pass through the material but it has to bend around the lines, which are about the size of a wavelength of visible light. Different wavelengths of light bend at different angles, so light that is made up of more than one color gets “spread out” into its fundamental colors when it passes through a diffraction grating. This phenomenon is known as… diffraction! So, when light hits the CD it’s reflected because of the shiny coating, but essentially diffracted because of the way it reflects off the track of zeros and ones that spirals around the bottom of the disc. And that’s how the white light that enters the slit in the side of the box becomes the spectrum of colors you see when you look through the eyehole.

So what’s the point? Well, it turns out that there’s a lot more to white light than meets the eye (unless that eye is looking through our cereal box spectroscope).

Written Response (15 points)

True or False: CFLs make objects, people, and environments look gray and dull compared with how they look under incandescent light or natural daylight. Defend your response. Include how the spectroscope you created explains this dilemma. Your answer should be ½ to 1 page in length.

Photo (15 points)

Take a photo of your spectroscope. Paste it into your report or upload the picture file with your assignment.