Laser Reflection - Gizmo Student Exploration

Name: Liyu Redda Date: Student Exploration: Laser Reflection Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: angle of incidence, angle of reflection, laser, law of reflection, plane mirror, reflection Prior Knowledge Questions (Do these BEFORE using the Gizmo.) Imagine you shine a flashlight directly at a mirror, as shown below. ✏️ 1.​ Click the image, click Edit Draw an arrow showing the direction you think the beam of light will most likely reflect off the mirror. ✏️ 2.​ Click the image, click Edit Suppose you tilt the mirror. Draw an arrow showing the direction the beam will most likely reflect off the mirror now. ​ Gizmo Warm-up Flashlights produce wide beams of light that have various wavelengths. A laser, on the other hand, is a narrow beam of light with only one wavelength. All the waves in a laser beam are parallel to one another. As a result, lasers are ideal for studying reflection, or how waves bounce off a surface. Using the Laser Reflection Gizmo, you can adjust the position of a laser beam and mirror to study how light behaves when it is reflected. 1.​ Drag the Angle slider back and forth. Describe what happens to the reflected laser beam: The reflected laser beam changes its angle of reflection. When the slider is moved to the left, the reflected beam moves to the left and when you move it to the right, the reflected beam moves to the right. 2.​ Drag the laser up and down. Describe what happens to the reflected laser beam: The position where the laser beam hits the mirror changes and the position of the reflected Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved laser beam moves up and down. Get the Gizmo ready: Activity A: Reflection from a plane mirror ●​ Set the Laser location to 0 cm. ●​ Set the Angle to 25 degrees. ●​ Make sure Plane mirror is selected. Introduction: A plane mirror is a perfectly flat, smooth surface. In this activity, you will study how plane mirrors reflect light. Question: How does the angle of a mirror determine the angle of the reflected light? 1.​ Observe: Turn on Show normal. The normal is the dotted line perpendicular to the mirror. The angle of incidence (θi) is the angle between the incoming laser beam and the normal. The angle of reflection (θr) is the angle between the reflected laser beam and the normal. Move the Angle slider back and forth. What do you notice about the sizes of θi and θr? The sizes of angle of reflection and angle of incidence are always equal to each other. 2.​ Measure: Set the Angle to 40 degrees and turn on Show protractor. Each marking on the protractor represents 10 degrees. What do θi and θr equal? θi = 40 θr = 40 3.​ Make a rule: What is the relationship between θi and θr? The angle of incidence is equal to the angle of reflection. This is known as the Law of Reflection. Turn on Show angles and move the Angle slider back and forth. Was your rule correct? Yes it is correct because the angles of incidence and reflection remain equal as I move the slider. The law of reflection states that the angle of incidence is equal to the angle of reflection. 4.​ Gather data: Use the Gizmo to complete the table below. Mirror angle Angle of incidence (θi) Angle of reflection (θr) 0° 25 25 25° 50 50 Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved ​​ 50° 75 75 5.​ Make a rule: How is the mirror angle related to the angles of incidence and reflection? The angle of incidence and the angle of reflection are both equal to the initial laser angle plus the mirror angle. Activity B: Reflection from non-planar mirrors Get the Gizmo ready: ●​ Turn off Show normal and Show protractor. ●​ Set the mirror Angle to 50°. Question: How can you use the angle of refraction to determine the shape of a non-planar mirror’s surface? 1.​ Observe: Turn on Insert beam splitter. How do the seven incoming beams compare with one another? How do the reflected beams compare with one another? The seven incoming beams are parallel to one another and the reflected beams are also parallel to one another. 2.​ Observe: From the dropdown menu at lower right, select Mirror 1. Unlike the plane mirror, mirror 1 is not flat. A.​ Describe how the laser beams changed: The reflected laser beams are no longer parallel to one another. They diverge or spread out after reflecting off the curved surface of Mirror 1. B.​ Why do you think this happened? This happened because the angle of the mirror’s surface is different at each point where the parallel incoming beams strike it. 3.​ Solve: Turn off Insert beam splitter. Set the mirror’s Angle to 0 degrees and the Laser location to 35 cm. Check that Show angles is on. A.​ What are the angle of incidence and angle of reflection (θi and θr)? The angle of incidence and angle of reflection equal to 0 degrees. B.​ What does this tell you about the surface of the mirror in this location? This tells you that at the point where the laser hits the mirror at a height of 35 cm, the surface of the mirror is perpendicular to the incoming laser beam. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved ​​ C.​ Move the Laser location to 14 cm. How did the orientation of the beam change? It will no longer be reflected directly back along the incident path because the height is no longer perpendicular to the laser beam. D.​ What does this tell you about the surface of the mirror in this location? The surface of the mirror is tilted relative to the incoming laser beam, causing the angle of incidence to be non-zero. 4.​ Summarize: What does it mean if the reflected beam is above the incident beam? What does it mean if the reflected beam is below the incident beam? It means the mirror’s surface at the point of reflection is angled in a way that directs the light upwards relative to the incoming beam. 5.​ Collect data: You will now use the laser to map the surfaces of mirrors 1, 2, and 3. In the rows of the table, record each mirror’s angle at all the listed locations. If the beam is deflected downward, the angle is negative. Otherwise the angle is positive. Height Mirror 1 Angle Mirror 2 Angle Mirror 3 Angle 35 cm 3.5 3.8 0 30 cm 5 2.5 5 25 cm 3.5 1.3 0 20 cm 0.8 0.3 4.8 15 cm 3.5 1.3 0 10 cm 5 2.5 5 5 cm 3.5 3.8 0 0 cm 0 5 5 -5 cm 3.5 3.8 0 -10 cm 5 2.5 5 -15 cm 3.5 1.3 0 -20 cm 0 0 0 -25 cm 3.5 1.3 0 -30 cm 5 2.5 5 -35 cm 3.5 3.8 0 Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved ​​ ✏️ 6.​ Draw: Click the image, click Edit Use the data you collected to create drawings of the mirrors’ surfaces in the boxes below. Be sure to pay attention to negative signs, which indicate the direction of the angle. 7.​ Analyze: Does the law of reflection hold true for mirrors that aren’t flat? Use the Gizmo to explore this question, and describe your findings. Mirror 1​ Mirror 2​ Mirror 3 Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved