This is the final regular Investigation of the LabLearner CELL Light and Optics. In it, students will continued their exploration of the Visible Spectrum and were introduced to the entire Electromagnetic Spectrum.

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A. Discuss students’ observations from Trial 1. Ask students to refer to Problem 2 in their Student Data Record.

1. Ask students the following questions about the unfiltered light from the flashlight.

a. Ask students: What did you shine the light on? The sheet of paper.

b. Ask students: What color did the light appear? Student answers may vary. The color of the light appeared to be white or without color.

c. Ask students: If the light is shining on the sheet of paper, how were you able to perceive the light? Student answers may vary. The light striking the paper was reflected by the paper into their eyes.

d. Ask students: Why did the light from the flashlight appear “white?” Student answers may vary. The light consists of all of the wavelengths that correspond to the colors of the Visible Spectrum. When all the colors of the Visible Spectrum are present, we perceive the color of the light as “white.”

2. Ask students the following questions about the light from the flashlight filtered by the three colored filters.

a. Ask students: Were the observed colors the same as the colors you predicted would be transmitted by the three filters? Student answers will vary.

b. Ask students: Which wavelengths were transmitted by each of the filters? The wavelengths corresponding to a shade of red light were transmitted by the red filter, the wavelengths corresponding to a shade of blue light were transmitted by the blue filter and the wavelengths corresponding to a shade of green light were transmitted by the green filter.

Note: In Investigation Four, students refracted white light with a prism and observed the colors of the Spectrum that were absorbed and transmitted by each filter.  From this, they concluded that the red color seen when using the red filter was the result of a combination of wavelengths of light corresponding to red, dark blue, and violet colors.  The answer above does not include this detail because it is not likely that students will remember the exact colors that combined to produce the red light seen through the red filter.  However, students’ answers should reflect the concept that the color of light seen through each filter is most likely the result of a combination of different wavelengths rather than a single wavelength or single color of the Visible Spectrum.

c. Ask students: Which wavelengths were absorbed by each of the filters? Student answers will vary. All wavelengths except the wavelengths corresponding to red light were absorbed by the red filter; all wavelengths except the wavelengths corresponding to blue light were absorbed by the blue filter; all wavelengths except the wavelengths corresponding to green light were absorbed by the green filter.

d. Ask students: Why were some colors of the Visible Spectrum missing from the light filtered by each of the three colored filters? Student answers will vary. Any light that is not transmitted by a colored filter will be absorbed by the filter and not transmitted.

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B. Discuss students’ observations from Trial 2. Ask students to refer to Problem 3 in their Student Data Record.

1. Ask students the following questions about how the colored water affected the light from the flashlight:

a. Ask students: What wavelengths were transmitted by the yellow water onto the paper? The wavelengths corresponding to the yellow color observed were transmitted onto the paper.

b. Ask students: What wavelengths were absorbed by the yellow water? All wavelengths except the wavelengths corresponding to the yellow color observed were absorbed.

c. Ask students: How did the yellow water act as a colored filter? Student answers will vary. Like a colored filter, the yellow water transmitted certain wavelengths of light corresponding to its color and absorbed all other wavelengths.

2. Ask students the following questions about how the colored water and the colored filters together affected the light from the flashlight:

a. Ask students: What color light did you observe when the red filter was held above the beaker of yellow water? The light was red.

b. Ask students: What color light did you observe when the blue filter was held above the beaker of yellow water? Student answers will vary. The light was colorless or gray.

c. Ask students: What color light did you observe when the green filter was held above the beaker of yellow water? The light was green.

d. Ask students: Based on your observations, which wavelengths and colors of light were not transmitted by the yellow water and the filters?  Short wavelengths or blue light.

e. Ask students: Which wavelengths and colors of light were transmitted by the filters and the yellow water?  Long wavelengths or red light and medium wavelengths or green light.

f. Ask students: Which wavelengths and colors of light are included in yellow light?  Long wavelengths or red light and medium wavelengths of green light.

g. Ask students: What rule describes the absorption and transmission of different wavelengths of the Visible Spectrum by colored filters? Any wavelengths that are not transmitted must be absorbed by the filter. The wavelengths that are absorbed are missing from the wavelengths that are transmitted.

h. Ask students: How do the wavelengths that are transmitted by a filter or colored water compare to the color of the filter or the color of the water? The wavelengths that are transmitted correspond to the color of the filter or the color of the water.

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C. Discuss students’ observations from Trial 3. Ask students to refer to Problem 4 in their Student Data Record.

1. Ask students: What wavelengths were transmitted by the yellow water onto the paper? The wavelengths corresponding to the yellow color observed were transmitted onto the paper.

2. Ask students: What wavelengths were absorbed by the yellow water? All wavelengths except the wavelengths corresponding to the yellow color observed were absorbed.

3. Ask students: What color does the water appear to your eyes? Yellow. 

    What color light is transmitted through the yellow water into your eyes? Yellow.

4. Inform students that when considering the perception of visible light, we perceive only those wavelengths and the corresponding colors that are not absorbed by an object.

a. If we look through a transparent object like colored water or a colored filter, we perceive only the wavelengths and the corresponding colors that are transmitted by the object.

b. If we look at, not through, a transparent object we perceive the wavelengths and the corresponding colors that are reflected from the object into our eyes.

c. The reflected wavelengths are perceived by our eyes as the color of the object.

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D. Discuss students’ observations from Trial 4. Ask students to refer to problem 5 in their Scientist Data Record.

1. Ask students the following questions regarding their observations of the cubes:

a. Ask students: What are the observed colors of the cubes? The black cube appears black, the red cube appears red, the blue cube appears blue, the green cube appears green and the white cube appears white.

b. Ask students: What are the colors reflected off of the cubes? Are they the same as the observed colors? Yes, the reflected colors are the same as the observed colors.

c. Ask students: What are the colors absorbed by the cubes? The black cube absorbs all colors resulting in no wavelengths being reflected. The red cube absorbs all colors except those that combine to create that particular shade of red; the blue cube absorbs all colors except for those that combine to create that particular shade of blue, and the green cube absorbs all colors except those that combine to create that particular shade of green. The white cube absorbs no colors resulting in all wavelengths being reflected.

2. Ask students the following questions regarding the use of the filters to view the cubes:

a. Ask students: Why did the cubes appear to reflect different colors of light when you viewed them through the filters compared to when you did not use the filters? Light reflected off of the cubes was then subject to transmission through the filters. The filters may have absorbed some of the wavelengths of light that were reflected so that only certain wavelengths were transmitted. The absorption of wavelengths by the filters changed the observed color of the cubes.

b. Ask students: Compare and contrast the colors you observed with the colors observed by another group member.  Why do you think your results were similar or different? Student answers may vary.  The way one person perceives color is not exactly the same as another person perceives color.  Color vision depends on the way that the retina is stimulated and how it detects colored light.  Everyone’s eyes are different, so everyone perceives colors differently.

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Cognitive Tool: Rules

Ask students: What rule describes how we perceive the color of a transparent or an opaque object? 

• Any wavelengths that are not absorbed must be reflected or transmitted by the object. 
• The wavelengths that are absorbed are missing from the wavelengths that are reflected by an opaque object, so the color of the object corresponds to the wavelengths that are reflected.
• When dealing with a transparent object, the wavelengths that are absorbed are missing from the wavelengths that are transmitted, so the color of the object corresponds to the wavelengths that are transmitted.  

3. Inform students that we see the color of opaque objects in a way that is similar to the way we perceive the color of transparent objects.

a. If we look at an opaque object we perceive only those wavelengths and the corresponding colors that are not absorbed by the object.

b. The wavelengths and the corresponding colors that are not absorbed by the object are reflected by the object into our eyes.

c. The reflected wavelengths are perceived by our eyes as the color of the object.

4. Ask students to answer Problem 6i in their Student Data Record. 

The problem asks: Why do we see a red sweater as red?