In Investigation Two of the LabLearner CELL Light and Optics, students will experiment with light beams and mirrors. They will explore the Law of Reflection and use a protractor to measure the angles of incidence and reflection.

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A. Begin the Investigation by reviewing the concepts from Investigation One. Prompt students’ prior knowledge by asking students to use the Recall Tool.

Ask students: What do we do when getting ready to learn something new? Students should realize that the Recall tool is appropriate.

Pose the following questions to prompt student recall about light:

1. Ask students: What happens to light when it strikes an object? Light is transmitted, reflected, or absorbed.

2. Ask students: What is the difference between transmission, absorption, and reflection of light? If light is transmitted, it is transferred from one place to another. If light is absorbed, it is taken in. If light is reflected, it bounces back from the surface of an object.

3. Ask students: In the first Investigation, which solution absorbed the most light? Solution C, the darkest in color absorbed the most light.

4. Ask students: Which solution transmitted the most light? Solution A, the lightest in color transmitted the most light.

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B. Divide the class into groups and instruct students to turn to their Student Data Record.

1. Ask student volunteers to read Problems 1a and 1b in their Student Data Record.

2. Allow student groups five to ten minutes to discuss and answer the questions.

3. Assist students by asking them to first think of substances or objects which transmit, reflect, or absorb light.

4. Ask students to then recall the experiments from Investigation One and to think of observations of real-life examples of the transmission, reflection, and absorption of light. Instruct students to record any combination of the three behaviors of light.

5. Ask student groups to share their answers to Problems 1a and 1b.

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C. Inform students that their groups will now discuss different relationships that deal with light.

1. Ask students to recall the relationships they investigated in Investigation One that related the terms shade, absorption, transmission, opaque, and transparent. Those relationships might include:

• Opaque substances absorb more light than transparent substances.

• Transparent substances transmit more light than opaque substances.

• Substances that are dark in shade absorb more light than substances that are lighter in shade.

• Substances that are lighter in shade transmit more light than substances that are darker in shade.

2. Ask student groups to use the Prediction Tool and think of relationships that might be true about surfaces and the reflection of the light off of the surfaces. If necessary, refer students to the definition of reflection in the Scientist’s Glossary. 

Ask students to record their predictions in Problem 2a and 2b in their Student Data Record.

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D. Inform students that throughout this CELL, they will be testing relationships between the reflection of light and different surfaces.  For the first test of how light is reflected, perform the following activity:

1. Ask one student from each group to remove the black and white sheet of paper from the last page of the Student Data Record from Investigation Two.

2. Ask students to observe whether the sheet is opaque or transparent and to record their answer in Problem 3a in their Student Data Record.

3. Ask students to observe whether the black and the white halves of the sheet are dark

or light in shade to record their answer in Problem 3b in their Student Data Record.

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4. Ask students to observe the chin of one of the students in their group. Instruct the student to hold the white half of the sheet directly under their chin. Ask the other students to observe the student’s chin and record any change in Problem 3c in their Student Data Record.

5. Ask students to repeat the procedure, this time instructing the student to hold the black half of the sheet under their chin. Ask students to observe the student’s chin and record any change in Problem 3d in their Scientist Data Record.

6. Ask students to answer Problem 3e in their Student Data Record.

7. Ask students to discuss their answer to Problem 3e. Discuss why placing the white and then the black half of the sheet under the student’s chin changed the appearance of the student’s chin.

8. Ask students to answer Problem 3f in their Student Data Record.

9. Ask students to discuss their answer to Problem 3f. Discuss any relationships between the reflection of light and the type of surface that the light strikes.

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E. Begin a discussion of angles to help their understanding of the Lab.

1. Ask students: In what direction did the light reflect up onto their chin? Student answers will vary. The light reflected up from the paper onto their chin.

2. Ask students: How would you describe the direction of the reflected light in a more exact way than just up? Student answers will vary. The light reflected up from the paper at an angle or a specific direction.

3. Ask students to stand up at their seats and face forward. Ask students to slowly turn in a circle until they are facing forward again.

4. Ask students: How would you describe your movement? Student answers will vary. Students will describe their movement as a circle or spinning. 

5. Ask students: Can you describe the circle more exactly? Student answers will vary. There are 360 degrees in the circle that they just turned. Every partial circle that they turn is a portion of the total of 360 degrees.

6. Ask students to again stand up and face forward and turn to face what was directly to their right. Inform students that they just turned 90 degrees or one-quarter of a circle.

7. Inform students that angles are measured in degrees which are certain portions of the total number of angles in a circle.

F. Inform students that in the Lab, they will investigate the reflection of light off a surface at specific angles by answering the following question:

• In what direction does light reflect off a surface?

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Protractor Practice: In this final slide, students can learn how to or refresh their memories of how to read the angles on a protractor similar to the ones they will use in Lab. There are four examples on this slide and the answers are shown below for you. Notice that this protractor has zero at the top of the arch and degrees can be determined both to the left and right up to 90^o.  Not all protractors are set up this way, but it is perfect for students to read the angle of incidence and angle of reflection quickly. A more typical protractor is shown below for reference.

Work with the class to determine the angles that are made by the red and black line with the horizontal. Notice that the angles can be read directly both to the left (left two examples) or the right (right two examples) of the zero.