Wrapping Things Up

Reflection and the Ray Model of Light

Objective:

Students will learn about how light and the relationship of an objects distance from a mirror affects an image’s reflection.

Timeline:

First Period – PowerPoint and lab activity

Second period – Assessment

5 Questions for the Final

1.      If a ray of light could be observed approaching and reflecting off of a flat mirror, then the behavior of the light as it reflects would follow a predictable law known as­__________?

a.       Law of Reflection

2. A ray of light is incident towards a plane mirror at an angle of 30-degrees with the mirror surface. What will be the angle of reflection?

b.      The angle of reflection is 60 degrees. (Note that the angle of incidence is not 30 degrees; it is 60 degrees since the angle of incidence is measured between the incident ray and the normal.)

3. The image of an object as formed by a plane mirror is located          .

a.  on the mirror surface                          b.  in front of the mirror surface

           c.  behind the mirror surface                  d.  any of the above, depending on the object's location

4. If Suzie stands 3 feet in front of a plane mirror, how far from the person will her image be located?

            a. Answer = 6 feet
Suzie (the object) is located 3 feet from the mirror. Suzie's image will be located 3 feet behind the mirror. Thus, the distance between Suzie and the image will be 6 feet.

5. Rose Inhatt stands between a set of parallel plane mirrors (M₁ and M₂) as shown in the diagram below. There is a flower on Rose's hat that is located a distance of 0.4 m from M₁ and a distance of 1.0 m from M₂. Since the mirrors are parallel, Rose will see an infinite number of images of the flower as she looks in mirror M₂. These images stretch towards infinity. Some of the images are closer to the mirror than others.

Determine the distance between mirror M₂ and the...

a. ... nearest image ____________

b. ... second nearest image____________

c. ... the third nearest image ____________

                a. 1.0 m, 1.8 m, and 3.8 m

Teacher Meeting

We will make a power point for a lecture.(The information will be gained from physcicsclassroom.com) Then a review worksheet will be handed out to reinforce what was just taught. After the review worksheet is handed out, a lab will be presented to the students.

Objectives:


Lab:

The Laboratory © The Physics Classroom, 2009 Plane Mirror Image Lab Teacher’s Guide Topic: Reflection and Mirrors The following information is provided to the student: Question: How does the distance from object to the mirror compare to the distance from the image to the mirror? Purpose: To compare the object's distance from the mirror to the image's distance from the mirror. A complete lab write-up includes a Title, a Purpose, a Data section, a Conclusion and a Discussion of Results. The Data section should include a mirror line (labeled), three sets of incident and reflected rays originating from the same location, extensions of reflected rays to show image location, and clearly labeled measurements of object and image distances. The Conclusion should respond to the question raised in the Purpose of the lab (as always). The Discussion of Results section should discuss the supporting evidence for the conclusion; should include a percent difference calculation for the image and object distance. Materials Required: Plane mirror with a vertical mount; cardboard sheet; push pin; laser light; sheet of paper; ruler or straight-edge. Description of Procedure: A line is drawn across the middle of a sheet of paper. The sheet of paper is placed on the cardboard sheet. A plane mirror is placed in an upright orientation on the sheet of paper. The reflecting surface of a plane mirror is aligned with the line. A push pin is pushed through the paper into the cardboard at a location of about 8-10 cm from the mirror. A leveling laser is set to LINE setting and placed with its flattest edge on the sheet of paper. The laser line is directed such that it passes through the push pin, hits the mirror and reflects. The path of the light is clearly evident on the paper since the LINE setting is being used. Students document the path of the both the incident and the reflected light on their paper. The process is repeated for two other unique laser paths. The laser is turned off and the mirror is removed. The three reflected rays are traced backwards to an intersection point. Students make measurements of the image distance and the object distance and answer the question posed in the Purpose of the lab. Alternative Materials and Procedure: If lasers are not available, a line of sight method which makes use of three pins can be implemented. One pin serves as the object. The other two pins are placed along a sight line as the student sights with one eye at the image of the object. The image of the object pin and the two sighting pins should all be in a perfect line. A straight edge can be used to trace the path of light from the mirror along the sighting line (through the two sighting pins). A second line can be drawn from the object to the mirror at the location where the sighting line hits it. This can be done for three different sighting lines and the image can be located as the intersection point of all three sighting lines. The Laboratory © The Physics Classroom, 2009 Safety Concern: There is always a higher than usual level of risk associated with working in a science lab. Teachers should be aware of this and take the necessary precautions to insure that the working environment is as safe as possible. Light from lasers should never be pointed into a person's eye. Caution should be taken to avoid such mishaps. Student horseplay and off-task behaviors should not be tolerated. Suggestions, Precautions, Notes: 1. Here are two methods for vertically mounting a plane mirror so that it stands upright on a sheet of paper. First, 1-inch thick strips of wood with the same dimensions as the mirrors can be cut and glued to the back of the mirrors. The wood must be perfectly flat along one of its edges. Second, large binder clips could be purchased and clipped to the bottom sides of your mirrors to provide a base of support. 2. Inexpensive leveling lasers can be purchased at a home store. They often go on sale for $5 during the Christmas season. They possess the capability of projecting the laser as a line or a beam. If the price is right, consider picking up a class set for use in both reflection and refraction activities. 3. Most inexpensive mirrors are coated with a reflective material on the back surface of a thin pane of glass. This does cause difficulties for many optics labs since the reflecting surface is actually behind the glass and not on the glass. A quick fix is to use a so-called two-way mirror which has its reflective coating on the front of the glass (actually, on both sides of the acrylic). An acrylic sheet can be purchased and cut into 3"x5" strips for a cost of approximately $2 per mirror. Avoid scratching the mirror during the cutting process. 4. This lab represents a great opportunity to begin reinforcing the concept of an image location as the location in space where it seems to every observer that reflected light is coming from. For this lab, that location is the location where all the reflected rays intersect when traced back behind the mirror. 5. This lab represents a great opportunity to pool class results. After completing their procedure and measurements, request that students come forward and write their group's do and di values on the board. With several data points, a suitable conclusion can be drawn. 6. Warn students in advance of the lab of the need to never direct laser light at another person's eye. Students who do not heed your warning should immediately be dismissed from the lab. Auxiliary Materials: None Scoring Rubric: RM2. Rough versus Smooth Lab Included, labeled and organized all parts of the lab report. Data section includes a wealth of observations pertaining to reflection of light off a mirror, dry paper and wet paper (diagrams would be useful); observations are labeled to distinguish between the surfaces observed; observations are clear, pertinent and understandable. Conclusion/Discussion describes the differences in reflection off the three types of surfaces. An accurate, reasonable and thorough explanation of the differences is provided. Score _____/_____ Connections to The Physics Classroom Tutorial: The following reading is a suitable accompaniment to this lab: http://www.physicsclassroom.com/Class/refln/u13l2a.cfm The Laboratory © The Physics Classroom, 2009 http://www.physicsclassroom.com/Class/refln/u13l2b.cfm Connections to Minds on Physics Internet Modules: Sublevels 2 and 3 of the Reflection and Mirrors module are suitable accompaniments to this lab:

Citations
"Plane Mirror Lab." The Physics Classroom. ComPADRE, 2009. Web. 3 Nov. 2013. <http://www.physicsclassroom.com/lab/refln/RM2tg.pdf>.

"The Role of Light to Sight." The Role of Light to Sight. ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l1a.cfm>.

"The Line of Sight." The Line of Sight. ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l1b.cfm>.

"The Law of Reflection." The Law of Reflection. ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l1c.cfm>.

"Specular vs. Diffuse Reflection." Specular vs. Diffuse Reflection. ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l1d.cfm>.

"Image Characteristics." Image Characteristics. ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l2b.cfm>.

"Ray Diagrams." Ray Diagrams. ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l2c.cfm>.

"What Portion of a Mirror Is Required?" What Portion of a Mirror Is Required?ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l2d.cfm>.

"Right Angle Mirrors." Right Angle Mirrors. ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l2e.cfm>.

"Other Multiple Mirror Systems." Other Multiple Mirror Systems. ComPADRE, n.d. Web. 30 Oct. 2013. <http://www.physicsclassroom.com/Class/refln/u13l2f.cfm>.

Worksheets
http://www.physicsclassroom.com/curriculum/refln/refln3.pdf
http://www.physicsclassroom.com/curriculum/refln/refln4.pdf
http://www.physicsclassroom.com/curriculum/refln/refln1.pdf

Proposal

Rebecca Kane, Sarah Dolan

Physics Research Project

Topic: Mirrors and Telescopes

We plan to start the lesson off with a lecture accompanied by a PowerPoint.  Along with the Power Point/ Lecture, students will be handed a note taking sheet to follow along. After the lecture is finished, a work sheet will be handed out to reinforce the information that was learned. Once completed, students will then be taken to the lab to experiment with mirrors. As students finish the lab, a quiz will be distributed to test their knowledge.