Gizmo Answers: Laser Reflection

Name: Date: Student Exploration: Laser Reflection 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. Draw an arrow showing the direction you think the beam of light will most likely reflect off the mirror. 2. 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 reflection moves up and down the _________________________________________________________________________ screen _________________________________________________________________________ 2. Drag the laser up and down. Describe what happens to the reflected laser beam: ________ Both the laser and the reflected laser move up and down. _________________________________________________________________________ 2019 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 values increase and decrease at the same rate. _________________________________________________________________________ 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? 40 θi = ____________ 40 θr = ____________ 3. Make a rule: What is the relationship between θi and θr? ____________________________ θi and θr are equal _________________________________________________________________________ Turn on Show angles and move the Angle slider back and forth. Was your rule correct? Yes, θi and θr are equal _________________________________________________________________________ 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) 0° 0 25° 25 50° Angle of reflection (θr) 0 25 50 50 5. Make a rule: How is the mirror angle related to the angles of incidence and reflection? Mirror angle is equal to the angle of incidence and reflection _________________________________________________________________________ 2019 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 nonplanar 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? Incoming and reflected beams are parallel. _________________________________________________________________________ _________________________________________________________________________ 2. Observe: From the dropdown menu at lower right, select Mirror 1. Unlike the plane mirror, mirror 1 is not flat. the reflected beams are now parallel A. Describe how the laser beams changed: ___________________________________ ___________________________________________________________________ Each incoming laser hit a different point B. Why do you think this happened? ________________________________________ on the not flat mirror ___________________________________________________________________ ___________________________________________________________________ 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. θi = 0° θr = 0° A. What are the angle of incidence and angle of reflection (θi and θr)? ______________ B. What does this tell you about the surface of the mirror in this location? ___________ The surface of the mirror at 35 cm is flat and perpendicular to the incoming beam. ___________________________________________________________________ C. Move the Laser location to 14 cm. How did the orientation of the beam change? The reflected beam changed direction, no longer reflecting straight back. It reflected at a new ___________________________________________________________________ angle, indicating that the angle of incidence increased and so did the angle of reflection. D. What does this tell you about the surface of the mirror in this location? ___________ ___________________________________________________________________ (Activity B continued on next page) 2019 Activity B (continued from previous page) 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? _________________________________________________________________________ This tells us the mirror’s surface is not flat at 14 cm—it is tilted or curved. The mirror has a different orientation at this point, which changes the angle of incidence and therefore the direction of the reflected 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 6. Draw: 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. Mirror 1 Mirror 2 Mirror 3 35 cm 30 cm 25 cm 20 cm 15 cm 10 cm 5 cm 0 cm -5 cm -10 cm -15 cm -20 cm -25 cm -30 cm -35 cm 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. _________________________________________________________________________ _________________________________________________________________________ 2019