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Solar Energy: Classroom Activities

Observing the Electromagnetic Spectrum


Goal

To recognize that visible light is a form of electromagnetic radiation that can be separated into a color spectrum.

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Background Information

Solar radiation is produced in the extremely hot core of the Sun. In a process called nuclear fusion, hydrogen atoms are fused together to form helium atoms. A very small quantity of mass is converted to energy in this process. This energy is radiated in all directions from the surface of the Sun as electromagnetic radiation. Electromagnetic radiation is energy that travels through space in the form of waves. The electromagnetic radiation that arrives at Earth from the Sun is mostly visible light, but much of the energy is also in the ultraviolet range (shorter wavelengths) and in the infrared range (longer wavelengths).

Visible light is made up of various colors, each with a different wavelength. This light can be observed using a spectrometer. When visible light waves are passed through a spectrometer, they are bent, or refracted, forming an unbroken band of colors called the visible spectrum. Red light has the longest wavelength, and violet has the shortest.

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Activity Overview

Students use a spectrometer to observe the visible part of the electromagnetic spectrum under natural sunlight, fluorescent light, and incandescent light.

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Materials and Equipment

Cardboard spectrometer, access to natural light, access to fluorescent light, access to incandescent light

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Activity

  1. Explain to students that they will use a spectrometer to observe light from the Sun. Provide them the following instructions:
    1. Never look directly at the Sun.
    2. Hold the end of the spectrometer with the diffraction grating to your eye.
    3. Direct the spectrometer toward a part of the sky away from the Sun.
    4. Look for a spectrum of colors along the side of the spectrometer.
  2. Ask students to describe the colors they observe.
    From left to right the colors observed are red, orange, yellow, green, blue, and violet.
  3. Have students move the spectrometer to the right and left. Ask them to describe their observations.
    The movement of the spectrometer has no effect on the order of the colors or the width of the individual color bands. Students will observe that the spectrum fades as the spectrometer is moved beyond the source of reflected sunlight.
  4. Instruct students to look through the spectrometer at a fluorescent light. Ask them to describe their observations.
    Students should observe that the order of colors is the same as in the reflected sunlight.
  5. Instruct students to look through the spectrometer at an incandescent bulb. Ask them to describe their observations.
    Students should observe that the order of colors is the same as in the reflected sunlight.
  6. Ask students to summarize their findings.
    Students should note that the order of colors did not differ in any of the three spectra. However, in the fluorescent light spectra, there were three narrow color bands (in the yellow, green, and violet parts of the spectrum) that were much brighter than the rest of the spectrum. (Note that depending on the type of fluorescent light bulb, this may vary.)

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