Physics courses that include Ray Optics as part of their curriculum will often spend time discussing refraction at the boundary of two materials. Understanding the refraction of light helps a student understand a wealth of phenomenon in the physical world. It provides students with the framework for understanding the (nearly) everyday observation of an object submerged in water when viewed with eyeballs located outside of the water. Most of these explanations are dependent upon an understanding of how light bends (i.e., which direction light bends) as it passes across the boundary from one material to another.

This Concept Builder is intended for use once a conceptual understanding of refraction and the direction of bending is well understood. The activities demand that a learner understand how the relative speed of light, relative optical density, or relative index of refraction of two materials affect the direction of bending. At The Physics Classroom, we utilize two simple rules by which to think about this direction of bending. We refer to these as the FST Rule (for fast to slow ... bends towards the normal line) and the SFA Rule (for slow to fast ... bends away from the normal line). Once a student has acquired an unerstanding of these two rules through lab exploration, demonstration, discussion, and practice, they are ready for this Concept Builder. We recommend it for use in the latter stages of the learning cycle on refraction and the direction of bending.

Each question includes three diagrams. Students must analyze each diagram carefully to determine which violate the law of refraction. That is, they must determine which illustrate the incorrect direction of bending. There can be more than one answer in each question. Students tap on the diagram to select and deselect it as an answer. Once they are satisfied with their selection, they can tap the Check Answer button. Their answer will be evaluated and feedback will be immediate.

The determination of the answers for each question will require considerable analysis and thought - the hallmark of our Concept Builders. Students must know their concepts and apply them. A successful student will be a student that will slow down, think, organize thoughts, jot down a note, reflect on their understanding, recognize mistakes and avoid them in subsequent exposures.

This Concept Builder was intended as an in-class activity. The Concept Builder includes 36 different questions that are organized into 12 different Question Groups and spread across four different activities. The first three activities focus on the affect of a single variable upon the direction of bending. The first activity focuses on the effect of the relative speed of light in the two media upon the direction of bending. The second activity focuses on the effect of the relative optical density of the two media upon the direction of bending. The third activity focuses on the effect of the relative index of refraction value of the two media upon the direction of bending. The last activity includes a mixture of each of the three variables upon the direction of bending. Teachers using the Concept Builder with their classes should preview the activity (or view the Questions in the separate file) in order to judge which activities would be most appropriate for their students. 

In order to complete an activity, a student must correctly analyze each situation in that activity. If a student's answer is incorrect, then the student will have to correctly answer the same or very similar question twice in order to successfully complete the activity. This approach provides the student extra practice on situations 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 situation. Once a star is earned, that situation is removed from the que of situations 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 situation and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the situation must be correctly analyzed one time in order to earn a star. Once every situation for an activity has been successfully analyzed, the student earns a trophy that 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-building tool 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 Concept Builder 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.