In Investigation Three, students continued their study of light and optics. In Lab, students worked with four mirrors to see an object that they would not otherwise been able to see.

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A. Begin a review of angles using the 360 Degree Circle (yellow) the Protractor (positioned atop the 360° circle).

1. Explain to students that angles are described using degrees. The º sign stands for degrees.

2. One way degrees can be defined is by assuming that there are 360 degrees in a complete circle.

3. Each subdivision of the circle has a degree value associated with it.

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4. Inform students that the 90º angle shown in the circle defines the corner of a wall in the classroom, the corner of a desk, or the corner of a book cover.

5. Inform students that the 180º angle shown in the circle describes a straight line like the edge of a wall in the classroom or the lines between tiles on the classroom floor.

6. Inform students that describing angles in terms of degrees allows them to exactly define angles.

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7. Introduce the Protractor and point out to students how the markings on the protractor they used in Investigation Two divided half a circle into to sections. Each section was 90º.

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B. Ask students to describe their solution to the problem in the Lab of viewing the bear without being able to view it directly.

1. Ask students to describe the placement of the mirrors and the path that the light took from the bear to the last mirror.

2. Ask student volunteers to draw the diagram from Problem 4 in their Student Data Record on the board. Student diagrams may not be significantly different from each other but slight variations may exist.

3. Discuss the path that the light took from the bear to the last mirror. Use a student drawing from the board or this slide to illustrate the Law of Reflection.

C. Ask students the following questions about the Law of Reflection.

1. Ask students: How would you describe the Law of Reflection? The Law of Reflection states that the angle of incidence or the angle at which light strikes an object equals the angle of reflection or the angle at which light is reflected off of the object.

2. Ask students to respond to the question in Problem 5 in their Student Data Record: How did the Law of Reflection allow you to see the image of the bear in the mirror at the back of the cave? A series of reflections was created using four mirrors. When the first mirror was positioned in front of the bear, students directed the light reflecting off the bear at a certain angle of incidence. The angle of the mirror directed the light at a specific angle of reflection toward the next mirror. The same method was used to position the other two mirrors, angling them so that the angles of reflection and incidence resulted in the light being reflected in the mirror at the back of the cave.

3. Ask students: What evidence from your experiments supports the Law of Reflection? For each mirror used to reflect the image of the bear to the mirror at the back of the cave, the angle of incidence was equal to the angle of reflection.

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D. Use one of the student diagrams of their experiment drawn on the board or this slide to illustrate the Law of Reflection.

1. Draw the path of the light from the bear to every mirror.

2. Using the light path reflecting off of every mirror, demonstrate that the angle of incidence equals the angle of reflection for every mirror.

3. Demonstrate to students how the multiple angles of incidence and angles of reflection contribute to their view of the bear.

4. Ask students: What real-life applications of using multiple mirrors can you think of? Students may think of periscopes, spyware, single-lens reflex cameras, telescopes, microscopes, etc.