Exploring the Colors of Light CAUTION! Do not look into a laser or at any reflections of the laser from shiny surfaces! Do not look into the sun or at any reflections of the sun from shiny surfaces! Question: Can you tell what colors are produced by a light source by just looking at the light with your eyes? Can you use the colors given off by a light source to tell what kind of source it is? Science facts Isaac Newton used a prism to separate sunlight (or "white" light) into the colors of the rainbow: Red, Orange, Yellow, Green, Blue, Violet. He showed that these colors cannot be further separated; they are fundamental colors of light. These colors make up the visible spectrum. Each color in the visible spectrum has a different wavelength. Red light has the longest waves and violet light has the shortest waves. RED GREEN BLUE Often the color that you see contains several of the fundamental colors of light. For example, a television screen or computer monitor displays many different colors, but if you look with a magnifier at the screen you will see only very tiny red, green and blue pixels. The combination of varying amounts of the three colors produces all the colors you see on the screen. In this experiment you will examine the colors radiated by several different sources of light. When the colors are displayed in order of wavelength we call it the spectrum of the light source. A rainbow is the spectrum of sunlight! You could use a prism for this experiment, but prisms are a little difficult to work with. Like a prism, a diffraction grating can break light into a spectrum. To get the clearest spectrum, you first need to construct a spectroscope, a device for looking at spectra. The tube of the spectroscope keeps out room light and the slit on the end lets you focus on one light source at a time. the PHOTON Projects www.photonprojects.org © New England Board of Higher Education, 2005
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Procedure: 1. Write your name on the tube. 2. Place the warning sticker on the tube 3. Use a tiny amount of glue on a toothpick and attach the slit to one end of the tube. WARNING
look in here light source
Slit cut in poster board
tube
grating
4. Look through the diffraction grating with the slit pointed toward the light. You will see a bright spot in the center that will have the same color as the light itself. On either side, you will see one or more light spectra -­‐ a full rainbow for a source like a light bulb and individual lines for streetlights or energy saving fluorescent bulbs. You may have to look quite a bit to the side of the central spot to see the spectra. Focus on one of these spectra and draw what you see on the data sheet. Spectrum Slit in the center Spectrum the PHOTON Projects www.photonprojects.org © New England Board of Higher Education, 2005
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Exploring the Colors of Light DATA 1. Type of light source___________________ Violet
Red
2. Type of light source___________________ Violet
Red
3. Type of light source___________________ Violet
Red
Conclusions: What kind of light source do you think made the mystery spectrum? Do the spectra of the colored sources contain only the color you see with your eye? That is, if you looked at a red light bulb, did it show other colors in the spectrum or just red? Do some light spectra have more colors than others? the PHOTON Projects www.photonprojects.org © New England Board of Higher Education, 2005
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