The topic of plane mirrors is typically not a lengthy topic in most Physics curricula. But when covered, two of the most important questions are typically:

The second of these two questions is addressed by this Concept Builder.

In this Who Can See Who? Concept Builder, students get plenty of practice identifying the images that can be seen from a given eye position. Every question involves the same two tasks - first, to determine the location of each of the five images; and second, to determine which of the five images can be seen from the given eye location. There are a total of 12 Question Groups. Questions in the same group have the same mirror length and position. The objects are roughly in the same location with one or two exceptions. The eye location changes from one question to the next for those within the same Question Group. There is no intended difference in difficulty between the 12 Question Groups. There are three levels of difficulty by which a student can progress through this activity. The difficulty levels differ only in ters of the number of questions which must be answered for each difficulty level. This Concept Builder was intended as an in-class activity. After some early lab investigation, some discussion and demonstrations of image formation and image sighting, allow students an opportunity to interact with the questions. 

In order to complete a level, a student must correctly analyze each question of that level. 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 level. This approach provides the student extra practice on questions for which they exhibited difficulty. As a student progresses through a level, a system of stars and other indicators are used to indicate progress on the level. 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 of a difficulty level 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 levels.

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 a few resources at The Physics Classroom website that serve as very complementary supports for Who Can See Who? Concept Builder. These include:
 

• Reading:
  Most students will find that  Lesson 2 of the Reflection and the Ray Model of Light Chapter of the Tutorial is a perfect accompaniment to this Concept Builder. In particular, the following two pages will be most helpful:
  
  Ray Diagrams
  
  What Portion of a Mirror is Required to View an Image
  
  
   
• 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 are a few activities in the Reflection and Mirrors section that would be useful complements to this activity. These include:
  
  Image Formation and Characteristics
  
  Ray Diagrams
  
  Visit Reflection and Mirrors section of the Curriculum Corner.
  
  
   

• 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 RM2 and RM3 of the Reflection and Mirrors 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 Reflection and Mirrors 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 lab makes a useful pre-cursor to this Concept Builder.
  
  Images Lab
  
  Visit The Laboratory
  
   

Additional resources and ideas for incorporating this Who Can See Who? Concept Builder into an instructional unit on Reflection and Mirrors can be found at the Teacher Toolkits section of The Physics Classroom website.  Visit Teacher Toolkits.