Laser Reflection SE

University:
Princeton University
Course:
PHY 103 | General Physics I
Academic year:

2024
Views:

0

Pages:

15
Author:

nima max

Name: Date: Oct. 22, 2024 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. Click the image, click Edit ? ? Draw an arrow showing the direction you think the beam of light will most likely reflect off the mirror. 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 Drag the Angle slider back and forth. Describe what happens to the reflected laser beam: The reflected laser beam reflects at an angle and moves is deflected up and down, as the mirror tilts. The direction of the beam either reflects downwards when the angle is negative, or reflects upwards when the angle is positive Drag the laser up and down. Describe what happens to the reflected laser beam: The reflected laser beam moves up and down with the laser. The location where the beam reflects moves, in line with the laser location Get the Gizmo ready: Set the Laser location to 0 cm. Activity A: Set the Angle Reflection from a plane mirror to 25 degrees. Make sure Plane mirror is selected. Observe : Turn on Show normal . The normal is the dotted line perpendicular to the mirror. The angle of incidence ( ? i ) is the angle between the incoming laser beam and the normal. The angle of reflection ( ? r ) is the angle between the reflected laser beam and the normal. It appears that “the angle of incidence” is equal to “the angle of reflection”. Although they get bigger the farther the angle is from 0 (either negative or positive), they changes at the same rate. Measure : Set the Angle to 40 degrees and turn on Show protractor . Each marking on the protractor represents 10 degrees. Make a rule : What is the relationship between ? i and ? r ? ?i and ?r are equal to each other Yes, this rule that they are equal is correct Gather data : Use the Gizmo to complete the table below. Mirror angle Angle of incidence (?i) Angle of reflection (?r) 0° 0 0 25° 25 25 50° 50 50 Make a rule : How is the mirror angle related to the angles of incidence and reflection? The mirror angle is equal to the angles of incidence and reflection Get the Gizmo ready: Turn off Activity B: Show normal and Reflection from non-planar mirrors Show protractor . Set the mirror Angle to 50°. 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? Unlike the laser beam without the splitter, there are now multiple beams coming from the one laser. The incoming beams are all straight and parallel to each other. The reflected beams are reflected parallel to each other, as well. This results in a uniform or exact/predictable formation of the laser beams, when in use with the beam splitter. Observe : From the dropdown menu at lower right, select Mirror 1 . Unlike the plane mirror, mirror 1 is not flat. Describe how the laser beams changed: They reflect in different/not parallel lines. It’s also more unpredictable than the previous, uniform look. I think this is because the mirror is not flat, so it’s reflecting on a curved/wavy surface of a mirror. Why do you think It’s hitting these different parts of the mirror that are angled and tilted in different directions, this happened? causing the beams to no longer be parallel, but have some go in more scattered directions! 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. What are the angle of incidence and angle of reflection ( ? i and ? r )? The angles are 3.5 What does this tell you about the surface of the mirror in this location? The mirror surface overall, is not flat and is slightly tilted down in this location Move the Laser location to 14 cm. How did the orientation of the beam change? The beam is instead reflected upwards, above the laser location What does this tell you about the surface of the mirror in this location? That the mirror is once again, not flat and has both upwards and downwards tilted parts on its surface. This means that at this location, the mirror is tilted upwards. 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? If the reflected beam was above the incident beam, that means that that part where the beam was reflecting on the mir ror, is tilted upwards. The mirror’s surface would be tilted in a positive angle. Meanwhile, if the reflected beam was below the incident beam, that means, that specific location on the mirror is tilted downwards. The surface of the mirror in these cases would be tilted in a negative angle. 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 - + neither (0) 30 cm - + + 25 cm - + neither (0) 20 cm neither (0) neither (0) - 15 cm + - neither (0) 10 cm + - + 5 cm + - neither (0) 0 cm neither (0) - - -5 cm - - neither (0) -10 cm - - + -15 cm - - neither (0) -20 cm neither (0) neither (0) - -25 cm - - neither (0) -30 cm - - + -35 cm - - neither (0) 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. 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. Yes, the law of reflection is still true for mirrors that are not flat. With the Gizmos, I tried out all 3 mirrors that aren’t flat, and with all 3, (having the mirror at an angle of 0), as I moved the laser location up and down, the angles of incidence and reflection still remained equal to each other, no matter what the laser location was