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Investigation Four introduces students to light waves, wavelength, and frequency.

INVESTIGATE

Trial 1

1. In this Trial, students will demonstrate how transparent objects such as colored filters transmit specific wavelengths of the Visible Spectrum while absorbing other, specific wavelengths. Wavelengths corresponding to the color of the filter are those wavelengths that are transmitted, while other wavelengths of the Visible Spectrum are absorbed. The wavelengths that are transmitted through the filter to our eyes result in our perception of a certain color.

Students will extend their investigation by analyzing how pairs of colored filters transmit and absorb specific wavelengths and how the combination of filters changes the colors we perceive. When two filters are combined, wavelengths corresponding to the color of the first filter are transmitted while other wavelengths of the Visible Spectrum are absorbed. Some of the wavelengths that are transmitted by the first filter are absorbed by the second filter since the colors of the two filters are not the same. This results in the absorption of most of the wavelengths of the Visible Spectrum. Thus, only a few wavelengths of light are transmitted through both filters. The color that we perceive corresponds to the wavelengths of light that pass through both filters. This Trial will support students in answering the following questions:

What is the relationship between absorption and transmission of the wavelengths of the Visible Spectrum?

What is the effect of colored, transparent objects on white light?

2. Students will first observe the light from the flashlight alone, then as it is transmitted through single filters, and then through pairs of filters that are held together. Students should be cautioned that when pairs of filters are used, they should be held together without any space between them.

3. Students should record their observations in Problems 1a through 1g and answer the question in Problem 1h in their Student Data Record.

Trial 2

4. In this Trial, students will analyze how a glass prism affects the light from the flashlight. The white light that is transmitted through an uncolored and transparent glass prism is refracted by the prism into the Visible Spectrum. This Trial will lead students to consider the following questions:

White light is composed of what wavelengths?

The Visible Spectrum is composed of what wavelengths of light?

How can white light be separated into its individual wavelengths?

5. Throughout Trial 2, students should refer to the diagram in Problem 2 in their Student Data Record.

6. Students may need to slightly adjust the positions of the flashlight and the paper so the light falls on the paper.

7. For Problem 2a of Trial 2, instruct students to position the flashlight in the center of the lab table and place the paper in position 1.

8. For Problem 2b of Trial 2, instruct students to position the prism in front of the flashlight so that one of its points faces the flashlight. The paper should be placed in position 2.

9. Students should record their observations and answer the questions in Problem 2 in their Student Data Record.

Trial 3

10. In this Trial, students will analyze how each of the colored filters affects the individual wavelengths of the Visible Spectrum as they exit from the prism. Those wavelengths that correspond to the color of each of the colored filters will be transmitted. The other wavelengths of the Visible Spectrum will be absorbed by each of the filters and will be missing from the Visible Spectrum. Since the prism is used in this Trial to separate white light into the Visible Spectrum, the absorption and transmission of individual wavelengths by each filter will be more easily observed. Students should consider these questions as they conduct Trial 3:

What is the relationship between absorption and transmission of the wavelengths of the Visible Spectrum?

Which wavelengths of the Visible Spectrum will be absorbed or transmitted by transparent, colored objects?

11. Throughout Trial 3, students should refer to the diagram in Problem 2 in their Student Data Record.

12. Instruct students to position the flashlight and the prism as they did in Trial 2. The paper should be placed in Position 2.

13. Students may need to slightly adjust the positions of the flashlight and the paper so the light falls on the paper.

14. Students should then place each of the single colored filters approximately 10 cm in front of the paper in Position 2 and observe the light that falls on the sheet of paper. The filter should be placed so that all of the light leaving the prism goes through the filter.

15. In order to discern the different wavelengths of light that are absorbed and transmitted through the filters, students should make their observations by stepping close to the paper to view the colors, rather than by observing the colors from the position of the flashlight.

16. Students should record their observations and answer the questions in Problem 3 in their Student Data Record.

Trial 4

In this final Trial, students will analyze how pairs of colored filters affect the individual wavelengths of the Visible Spectrum as they exit from the prism. Wavelengths that correspond to the perceived color of the first filter are transmitted while the other wavelengths of the Visible Spectrum are absorbed. Some of the wavelengths that are transmitted by the first filter are absorbed by the second filter since the colors of the two filters are not the same. This results in the absorption of most of the wavelengths of the Visible Spectrum and transmission of only a few wavelengths of light through both filters. In conducting this Trial, students will answer the following questions:

What is the relationship between absorption and transmission of the wavelengths of the Visible Spectrum?

Which wavelengths of the Visible Spectrum will be absorbed or transmitted by transparent, colored objects?

18. The wavelengths of light that are absorbed and transmitted by both filters should be more obvious to students than in Trial 1 since the prism will have refracted the light from the flashlight into the Visible Spectrum.

19. Throughout Trial 4, students should refer to the diagram in Problem 2 in their Student Data Record.

20. Instruct students to position the flashlight and the prism as they did in Trial 3. The paper should be placed

in Position 2.

21. Students may need to slightly adjust the positions of the flashlight and the paper so the light falls on the paper.

22. Students should then place each pair of colored filters approximately 10 cm in front of the paper in Position 2 and observe the light that falls on the sheet of paper. The filter should be placed so that all of the light leaving the prism goes through the filter.

23. In order to discern the different wavelengths of light that are absorbed and transmitted through the filters, students should make their observations by stepping close to the paper to view the colors, rather than by observing the colors from the position of the flashlight.

24. Students should record their observations and answer the questions in Problem 4 in their Student Data Record.

25. On completion of the Investigation allow sufficient time to return all materials to the correct location in the Lab for storage.

KEYS

CLEAN UP

Let students know your expectations for clean-up. Ask them to clean up.