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Overhead Spectroscopy

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Author Contact Information

Linda Wygoda
Sam Houston High School
Lake Charles, Louisiana
wygoda@tea.rice.edu

Overview
In this demonstration activity, an overhead projector, diffraction grating and a series of filters are used to introduce the basic concepts of the visible electromagnetic spectrum and the relationship between wavelength and absorption of light. The overhead projector is used to project the spectrum from the diffraction grating on the board or wall. A series of colored filters are used to filter the light passing through the diffraction grating. The affects of the filter on the displayed spectra bands can be observed.

Students will

  • predict the color of an object through a colored filter

  • list the colors absorbed and transmitted based on the observed color of an object behind a filter

    Grade Level/Discipline
    High School 9-12; physics, chemistry, physical science

    National Standards
    Science Content Standard B: Interactions of energy and matter

    Pre-activity set-up
    1. Prepare a piece of cardboard to completely cover the projection panel of the overhead projector.

    2. Cut a small, approximately 1cm2 hole in the center of the cardboard cover.

    3. Prepare small colored filters to place over the 1cm2 hole in the cardboard cover.

    4. Attach the light probe of the calculator to a 15 cm ruler with tape.

    5. Attach the diffraction grating to the front of the projection lens of the overhead projector.

    Materials

  • overhead projector;
  • large diffraction grating
  • filters of various colors
  • cardboard to cover the projection panel of the
  • overhead

    Time Frame
    1 class period

    Engagement and Exploration (Student Inquiry Activity

  • If available in your classroom, show students the color enhanced images of NASA’s Earth Observation website: http://earthobservatory.nasa.gov/Observatory/.

  • From this site, ask the students how they think scientists obtain images of the atmosphere that show information about the ozone layer.

  • Discuss with the students that scientists travel to Antarctica to set-up instruments designed to identify and measure chemicals in the atmosphere that may impact the ozone layer and the Earth’s atmosphere.

  • Use the TEA website at: ../../tea_wygodafrontpage.html to obtain more information about research using the infrared spectrometer.

  • Ask the students the following question "Why is the electromagnetic spectrum an important tool in the study of global changes? Why is Antarctica an ideal place to use the tools of the electromagnetic spectrum for research?

  • Make a list of the student responses on the board for reference and further investigation.

  • Ask the students "How do you think scientists measure a phenomena that is not directly observable such as the wavelength of electromagnetic waves?"

  • Make a list of student responses and talk about ways these measurements can be made in the classroom.

  • Turn on the projector and dim the lights. What do the students see? As a class, observe the continuous spectrum that is projected.

    Explanation (Discussing)

  • What happens when different filters are applied? As a class, observe the different absorbtion patterns for the various colored filters.

  • The red filter will reflect light in the red wavelenths but light in the green wavelengths will be absorbed. This will appear as a black band in the green wavelengths.

  • The orange filter reflects light in the orange wavelengths but absorbs light in the blue wavelength.

  • Compare each colored filter with that produced from the continuous spectrum.

    Elaboration (Polar Applications)

  • Refer to ../../wygoda/12.9.1996.html and ../../wygoda/12.13.1996.html for additional information about the use of wavelengths in the analysis of the atmosphere.

  • Show diagrams or pictures of the other parts of the spectrum, including the infrared, microwave, ultraviolet,cosmic rays, radio waves, TV waves,AM radio waves

    Exchange (Students Draw Conclusions)

  • Have students make predictions for a parcticular filter and then as a class, test and observe the results. For example, what will be the effect of applying a blue filter? What colors will be absorbed, and what colors will be transmitted?

    Evaluation (Assessing Student Performance)

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