Introduction to Color 2

Building A Simple Spectroscope

A basic hand-held spectroscope can be made from a diffraction grating and a paper tube.

Objective:

To construct a simple spectroscope with a diffraction grating and use it to analyze the colors emitted by various light sources.

Materials:

Diffraction grating, 2-cm square
Paper tube (tube from toilet paper roll)
Poster board square (5 by 10-cm)
Masking tape
Scissors
Razor blade knife
2 single-edge razor blades
Pencil

Procedure:

1. Using the pencil, trace around the end of the paper tube on the poster board. Make two circles and cut them out. The circles should be just larger than the tube’s opening.

2.Cut a 2-centimeter square hole in the center of one circle. Tape the diffraction grating square over the hole.

3. Tape the circle with the grating inward to one end of the tube.

4. Make a slot cutter tool by taping two single- edge razor blades together with a piece of poster board between. Use the tool to make parallel cuts about 2 centimeters long across the middle of the second circle. Use the razor blade knife to cut across the ends of the cuts to form a narrow slot across the middle of the circle.

5. Place the circle with the slot against the other end of the tube. While holding it in place, observe a light source such as a fluorescent tube. Be sure to look through the grating end of the spectroscope. The spectrum will appear off to the side from the slot. Rotate the circle

with the slot until the spectrum is as wide as possible. Tape the circle to the end of the tube in this position. The spectroscope is complete.

6. Examine various light sources with the spectroscope.
If possible, examine nighttime street lighting. Use particular caution when examining sunlight. Do not look directly into the Sun.

Background:

Simple spectroscopes, like the one described here, are easy to make and offer users a quick look at the color components of visible light. Different light sources (incandescent, fluorescent, etc.) may look the same to the naked eye but will appear differently in the spectroscope. The colors are arranged in the same order but some may be missing and their intensity will vary. The appearance of the spectrum displayed is distinctive and can tell the observer what the light source is.

A diffraction grating can spread out the spectrum more than a prism can. This ability is called dispersion. Because gratings are smaller and lighter, they are well suited for spacecraft where size and weight are important considerations. Most research telescopes have some kind of grating spectrograph attached. Spectrographs are spectroscopes that provide a record, photographic or digital, of the spectrum observed.

Many school science supply houses sell diffraction grating material in sheets or rolls. When using the spectroscope to observe sunlight, students should look at reflected sunlight such as light bouncing off clouds or light colored concrete. Other light sources include streetlights (mercury, low-pressure sodium, and high-pressure sodium), neon signs, and candle flames.
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