Teacher Notes for Ray Optics

Lesson Plans || Learning Outcomes and Activities || Teacher Notes || Labs

 

Unit Overview

We would suggest that 20 days on this topic would be necessary to cover all Learning Outcomes. There are three primary goals:
 

1. To understand why the reflection of light off a smooth, flat surface results in the formation of an image.
2. To understand why the reflection of light off a concave or convex surface results in the formation of an image.
3. To use a qualitative approach to describe how the object location affects the image characteristics for plane, concave, and convex mirrors.
4. To understand the conceptual nature of light refraction at the boundary between two media.
5. To understand the conditions under which light undergoes total internal reflection at a boundary or undergoes partial reflection and partial refraction at a boundary.
6. To use qualitative approaches to describe how the object distance affects the image characteristics for converging and diverging lenses.

The first 5 days will be devoted to plane mirrors. The next 4 days will be devoted to curved mirrors. After the first 9 days, there are 7 days devoted to refraction and total internal reflection. The unit ends with 4 days of lenses.



 

Math

We have reduced the math complexity considerably in this unit. We have skipped the mirror equation and the lens equation. We do suggest a Snell's Law lab where a relationship between angles of incidence and refraction is derived from lab data. This can be facilitated by collecting class data into a spreadsheet (e.g., a Google Sheets) that has a couple of pre-set graphing options - θ_water vs. θ_air and sine θ_water vs. sine θ_air. Students can use observations and regression statistics to identify the equation that best describes the relationship. Yet they may have a weak to non-existent understanding of what sine means. The equations is used in a later lab in which the index of refraction is determined by making measurements of the two angles. We recommend the use of a sine table in situations in which students have little to no familiarity with this topic. Removing these two labs from the unit will remove the math entirely from the unit. Given the background of the typical student in a Conceptual Physics course, it wouldn't be a bad idea to make such a decision.



 

Labs!!

This unit is as phenomenological as they come. Every outcome can begin with a lab or demonstration. The hands-on experiences do not require fancy equipment. We've suggested 11 labs on our Learning Outcomes page. Eight of these labs have been used in our other courses; details for those labs are on our Lab Page for this unit; see the links to the Teacher's Guides  Labs 2, 5, and 6 cannot be found on our site so we have provided further details below.
 

Lab 1: Lab 1 is identical to a lab that we have used for our other courses. We have provided a link to the Teachers Guide on our Lab Page.

Lab 2: Lab 2 relies on a half-silvered mirror with large binder clips to hold it upright on a sheet of paper, two inexpensive tea light candles, and a ruler and protractor. Students place a candle in front of the upright mirror and trace around it; this is the object. They place the second candle behind the mirror; being half-silvered, they can look through the mirror and faintly see it. They look into the mirror from the front and maneuver this candle until it positioned at a location that aligns with the image of the object candle. They trace around the behind-the-mirror candle; this is the image. Students can then remove the candles and the mirror for the remainder of the lab. They draw four incident rays using a ruler - two on each side of the object - from the object candle's center towards the mirror with a direction such that the rays would strike the mirror. At the point of incidence, students construct a normal line, measure and angle of incidence, and accurately construct a reflected ray with the same angle. Arrowheads are placed on all 8 rays. Now students extend all refracted rays backwards to an intersection (or close-to-intersection) point. They can easily be led to the conclusion that the image location is the one location where it seems to all observers as though the light is coming from. Students make measurements of distances from to object and to image and finish up their Conclusion/Discussion. A pandemic era video of this lab can be found here.

Lab 3: Lab 3 is identical to a lab that we have used for our other courses. We have provided a link to the Teachers Guide on our Lab Page.

Lab 4: Lab 4 is identical to a lab that we have used for our other courses. We have provided a link to the Teachers Guide on our Lab Page.
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Lab 5: Lab 5 requires the use of a small concave mirror (preferably 40 cm < R < 60 cm) , a vertical stand for the mirror, a meter stick, a frosted night light bulb and receptacle (with a smiley face inscribed on the bulb with a Sharpie marker), a note card (to project images onto), and an F and C card. F and C cards can be constructed as 1 cm x 1 cm note card sections with the letters C and F printed on them; place some adhesive on the back so that they can be secured to the lab table. Students create an optics bench by placing their mirror at one end of their lab space and aligning the meter stick so that it extends outward from the mirror. The Smiley face light bulb can be placed at the opposite end of the meter stick. Students can be given the fact that the object and image for a concave mirror will be located at the same location and be of the same size when the object is at the focal point. Show students how to focus the image of the light bulb on the note card; do this for several different object locations.
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Lab 6: Lab 6 requires the use of the line setting on a leveling laser, a rectangular prism (lucite, glass, etc.), a straight-edge, and a sheet of paper. Students place the prism on the paper and trace around it. They shine the laser light into one side of the prism such that it refracts upon entry into and exit out of the prism. Using a pencil, they dash the path of light at several points. After turning off the laser and removing the prism, they can draw the entire path as light rays with arrowheads. Normal lines are constructed at each boundary. They are given relative speeds of light in air versus the prism material. From the data, they can reason towards a fast-to-slow refraction rule and a slow-to-fast refraction rule. They can make the same conclusions based on optical density.
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Lab 7: Lab 7 is identical to a lab that we have used for our other courses. We have provided a link to the Teachers Guide on our Lab Page.
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Lab 8: Lab 8 is identical to a lab that we have used for our other courses. We have provided a link to the Teachers Guide on our Lab Page.
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Lab 9: Lab 9 is identical to a lab that we have used for our other courses. We have provided a link to the Teachers Guide on our Lab Page.
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Lab 10: Lab 10 is identical to a lab that we have used for our other courses. We have provided a link to the Teachers Guide on our Lab Page.
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Lab 11: Lab 11 is identical to a lab that we have used for our other courses. We have provided a link to the Teachers Guide on our Lab Page.​

 

Other Resources

There are a few resources that we did not list in our Lesson Plans and Learning Outcomes and Activities that you may find to be very helpful. These include:
 

1. Science Reasoning Center: Curved Mirrors
   Students analyze and interpret a complex diagram; identify the effect of variations in one quantity upon another quantity; draw conclusions that are supported by one or more data presentations; identify evidence that supports a conclusion; transform data from a table into a graph; and to interpolate and extrapolate from data in a table.
2. Science Reasoning Center: Object-Image Relationships
   Students identify the effect of one variable upon another variable; select values and compare values on a graph; draw conclusions that are consistent with a data presentation (or two); combine data from two graphs in order to identify an accurate conclusion; and to interpolate using values on a graph.

 

 

Teacher Presentation Pack

We say this a lot. But we think it is worth saying. Our Teacher Presentation Pack is a huge time-saver. For early-career and cross-over Physics teachers, it may also become a life saver. It includes a large collection of Slide Decks, animations, and graphics for use in your classroom. Once downloaded, you can modify and customize the Slide Decks as needed. The slides are highly organized and (mostly) graphical; they make great graphic organizers for any student, and especially for the struggling student. Learn more.


 

Also Available ...

Physics teachers may find the following for-sale tools to bes useful supplements to our Lesson Plan and Pacing Guide section:

 

1. Task Tracker Subscription (annual purchase)
   A subscription allows teachers to set up classes, add students, customize online assignments, view student progress/scores, and export student scores. Task Tracker accounts allow your students to begin assignments in class or at school and to finish them at home. View our Seat and Cost Calculator for pricing details.
    
2. The Solutions Guide
   We publish a free curriculum with >200 ready-to-use Think Sheets for developing physics concepts. The Solutions Guide is a download containing the source documents, PDFs of source documents, and answers/solutions in MS Word and PDF format. An expanded license agreement is included with the purchase. (Cost: $25 download)
    
3. Teacher Presentation Pack
   This is a large collection of downloadable content packed with nearly 190 Microsoft PowerPoint slide decks, the corresponding Lesson Notes (as PDF and fully-modifiable MS Word format), about 170 animations (in .gif, .png, and .mp4 file formats), a countless number of ready-to-use images (including the original source documents that would allow for easy modification of those images), and a license that allows teachers to modify and use all the content with their classes on password-protected sites (such as course management systems).  (Cost: $40 download)
    
4. Question Bank
   We distribute a Question Bank that includes more than 9300 questions neatly organized according to topic. The Question Bank is the perfect tool for busy teachers or new teachers. Even if you don't use the website with your classes, the Question Bank will assist you in quickly putting together quizzes, tests and other documents with high-quality questions that target student's conceptions of physics principles. And if you do use The Physics Classroom website, the Question Bank is the perfect complement to the materials found at the website. (Cost: $25 download)