This is the first Investigation in the LabLearner CELL Light and Optics. Students will observe that the amount of light that is transmitted or absorbed depends upon the shade of the object.

Students will also investigate how transparent objects are able to reflect, transmit and absorb light, while opaque objects absorb or reflect but cannot transmit light.

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A. Begin a review of the Investigation.

1. Ask students the following questions:

• How did you test how much light was transmitted through each of the solutions? Students used the flashlight to shine light through each of the solutions onto a piece of paper. By observing the amount of light that shone on the paper, students determined how much light was transmitted through each solution.
• How did you test how much light was absorbed by the liquid in each of the three beakers? Students tested absorption in the same way. Students observed the amount of light that shone through each solution onto the piece of paper.

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B. As a class, discuss the data from the Investigation. Instruct students to refer to the table in Problem 3b in their Student Data Record.

1. Before students discuss the data, briefly review the terms transmit and absorb by reviewing the role-play performed during the. When light is transmitted, it is transferred from one place to another or it passes through a substance. When light is absorbed, it is taken in and does not pass through a substance.

2. Ask students to recall the shades of green of each of the three solutions. Instruct students to place the three beakers on the continuum in Problem 6 in their Student Data Record.

3. Ask students: Which solution absorbed the most light? Solution C absorbed the most light.

4. Instruct students to locate the absorb and transmit continuum in Problem 7 in their Student Data Record. Instruct students to use their experimental data from the Table to place Solution A, Solution B, and Solution C on the continuum.

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C. Discuss with the class the terms opaque and transparent, relating the terms to the Investigation.

1. Briefly discuss the definitions of the terms: 

An object that is opaque blocks the transmission of all light. 

An object that is transparent is able to transmit light.

2. Ask students to look around the classroom for examples of objects that are opaque and transparent. 

Examples of opaque objects include books, desks, students, and walls.

Examples of transparent objects include window glass, eyeglass lenses, clear plastic pens, and pencils.

3. Ask students to recall the appearance of the three solutions. Instruct students to work in pairs to recall which of the three solutions was most transparent and which was most opaque. Instruct students to record their conclusions on the continuum in Problem 8 in their Student Data Record.

4. After students have completed the continuum, ask the class the following questions to assess their understanding:

Ask students: Which solution was most transparent? Solution A was most transparent.

Ask students: Which solution was most opaque? Solution C was most opaque.

Note to Teacher: It is necessary that students correctly complete each of the three continua. If students have incorrectly completed any of the three, discuss any misconceptions and allow students to correct their answers.

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D. Divide the class into groups of two or three. Inform students that they will discuss any patterns that they can see in the data they have recorded for Solutions A, B, and C.

1. Instruct the groups to study the three continua in Problems 9, 10, and 11 in their Student Data Record. Inform students that they should use the data recorded in the continua to find any relationship among the following characteristics of the three solutions: the shade of the solutions, whether the solution absorbs or transmits light, and whether the solution was opaque or transparent.

2. Allow student groups approximately five minutes to discuss their data and to record the relationships that they have found in Problem 12 in their Student Data Record.

3. After students have recorded their answers, allow student groups to share their conclusions with the class.

4. Ask students: What relationship among the three solutions did you find? Student answers will vary. The darker the color of the solution, the more opaque the solution and the more light it absorbed. The lighter the color of the solution, the more transparent the solution and the more light it transmitted.

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E. Discuss whether these relationships can be generalized to all objects.

1. The relationships listed should be similar to the relationships that students found in their experimentation in the lab.

• • The opaque liquids are darker in shade.
  • The opaque liquids absorb more light.
  • The transparent liquids are light in shade.
  • The transparent liquids transmit more light.
  • The liquids which are lighter in shade transmit more light.
  • The liquids which are darker in shade absorb more light.

2. Inform students that they should work in their groups to determine if these relationships can be applied to substances or objects other than the solutions they studied in the lab. Instruct students to find objects in the classroom that follow or break these relationships.

3. After students have had adequate time to explore these relationships, ask student groups to share their findings.

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F. Inform students that they can also analyze the relationships in how light interacts with objects by analyzing the second experiment in Trial Two. To prompt students’ recall, ask the following questions:

1. Ask students: Describe the experiment in which the lamp was used to illuminate the black and white piece of paper. Students placed a black and white piece of paper under the shade of the lamp. After approximately ten minutes, a student felt the difference in temperature between the two halves of the paper.

2. Ask students: Were the two halves the same temperature? The black half of the paper was warmer than the white half of the paper.

3. Why was the black half of the paper warmer than the white half? Student answers will vary.

• • Ask students to recall the Law of Conservation of Energy. What does this law state concerning the energy that the light bulb emitted? The energy was not destroyed. It must have been transferred and changed form.
  • Ask students: What do you think happened to the heat energy that the light bulb emitted? Was heat energy the reason that the black half of the paper was warmer than the white half? Student answers may vary. The heat energy given off by the light bulb was absorbed by the paper and the table top and was dispersed in the air. The black half and the white half were exposed to the light for equivalent amounts of time and to the heat energy given off by the light bulb. Color does not affect the amount of heat energy that is absorbed by a substance. If only heat energy was given off by the light bulb, both sides of the paper would have been the same temperature.
  • Ask students: What do you think happened to the light energy that the light bulb emitted? Student answers may vary. If light is not transmitted, it is either absorbed or reflected, or both. The black half of the paper absorbed light energy due to its darker shade. The white half of the paper reflected light energy due to its lighter shade.
  • Ask students: What happened to the light energy after it was absorbed by the dark half of the paper? The light energy was converted to heat energy, which was detected by the student volunteer as an increase in the temperature of the black half compared to the white half of the paper.

4. Inform students that throughout the CELL, the class will be discussing relationships in the interaction of light with different objects. Some relationships are true in a many situations, while others depend on the circumstances and on the objects that interact with light.