Teachers who include units on the topics of reflection and refraction in their curriculum will often spend some time discussing the phenomenon of total internal reflection. The phneomenon occurs when light is in a more optically dense material and approaching the boundary with a less optically dense material with an angle of incidence that is greater than the critical angle. Provided that these two conditions are met, the light ray will undergo total internal reflection (TIR). This phenomenon is an alternative to the more usual occurence of a portion of the energy undergoing transmission across the boundary and a portion undergoing reflection off the boundary. The use of some form of demonstration materials provides students with the opportunity to view the two distinctly different phenomenon - total reflection vs. the dual combination of reflection and refraction.

The Total Internal Reflection Concept Builder seeks to assess student understanding of ...

There are three different activities that can be engaged in through the Concept Builder. The three activities are described as follows:

• To TIR or Not To TIR: Question Groups 1-4. Students are given comparative information about the two media and must identify any diagram that portrays an incident ray that would undergo TIR.
• R&R or TIR: Question Groups 5-8. Students match three different types of boundary behaviors to the relationship between the angle of incidence and the critical angle.
• Angle is Critical: Question Groups 9-12. Students are given comparative information about the two media and a critical angle and must identify any diagram that portrays an incident ray that would undergo TIR.

There are a total of 12 Question Groups. Questions in the same group are very similar in nature. In order to complete an activity, a student must correctly analyze each question in that activity. If a student's analysis is incorrect, then the student will have to correctly analyze the same or very similar question twice in order to successfully complete the activity. This approach provides the student extra practice on questions for which they exhibited difficulty. As a student progresses through an activity, a system of stars and other indicators are used to indicate progress on the activity. A star is an indicator of correctly analyzing the question. Once a star is earned, that question is removed from the que of questions to be analyzed. Each situation is color-coded with either a yellow or a red box. A red box indicates that the student has incorrectly analyzed the question and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the question must be correctly analyzed one time in order to earn a star. Once every question in an activity has been analyzed, the student earns a trophy which is displayed on the Main Menu. This system of stars and trophies allows a teacher to easily check-off student progress or offer credit for completing assigned activities.

The most valuable (and most overlooked) aspect of this Concept Builder is the Help Me! feature. Each question group is accompanied by a Help page that discusses the specifics of the question. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise. 

 

 

There are several resources at The Physics Classroom website that serve as very complementary supports for the Total Internal Reflection Concept Builder. These include:
 

• Reading:
  Most students will find that  Lesson 3 of the Refraction and the Ray Model of Light Chapter of the Tutorial is a perfect accompaniment to this Concept Builder. The three pages in the Lesson include:
  
  Boundary Behavior Revisited
  
  Total Internal Reflection
  
  Critical Angle
  
  
  
   
• Curriculum Corner
  The Curriculum Corner section of our website contains a complete course curriculum that coordinates with our Tutorial section and our Minds On Physics program. There is one particular activity in the Refraction and Lenses section that would make a useful complement to this activity. 
  
  Total Internal Reflection
  
  Visit Refraction and Lenses section of the Curriculum Corner.
  
  
  
   
• Physics Interactives
  The Physics Interactives section of our website consists of a collection of interactive simulations. The variable-rich environments of the simulation allows a student to explore and interact with a physical situation. One of the simulations - titled Refraction - provides an exceptional opportunity for students to explore the behavior of a light ray at the boundary between two materials. The Physics Classroom has prepared a classroom-ready activity for use with the simulation. View Total Internal Reflection activity.
  
  Visit Refraction Interactive.
  
  
   

• Minds On Physics Internet Modules:
  The Minds On Physics Internet Modules include a collection of interactive questioning modules that help learners assess their understanding of physics concepts and solidify those understandings by answering questions that require higher-order thinking. Assignments RL5 and RL6 of the Refraction and Lenses module is a great complement to this Concept Builder. It is best used in the middle to later stages of the learning cycle. Visit the Minds On Physics Internet Modules.
  
  Users may find that the App version of Minds On Physics works best on their devices. The App Version can be found at the Minds On Physics the App section of our website. The Refraction and Lenses module can be found on Part 6 of the six-part App series. Visit Minds On Physics the App.
  
  
   
• The Laboratory:
  There is no substitute for hands-on activities. And at The Physics Classroom, those hands-on activities can be found in The Laboratory section of the website. The following labs make for useful pre-cursors to this Concept Builder.
  
  R and R Lab
  
  A Critical Lab
  
  Visit The Laboratory.
  
   

Additional resources and ideas for incorporating this Total Internal Reflection Concept Builder into an instructional unit on Refraction and Lenses can be found at the Teacher Toolkits section of The Physics Classroom website.  Visit Teacher Toolkits.