New Perspectives in Science Education

The light rays are used as a basic tool to illustrate the formation of shadows and image in geometrical optics. By using only two special rays, teachers and textbooks can interpret the position and size of the images clearly. However, many researches have indicated that the representation of light rays is very abstract for students, and they have many difficulties in drawing and interpreting ray diagrams. Furthermore, a number of studies even have found that many students, including high school and college students, fail to explain the phenomena of shadow through the approach of light rays. Most of the students use an ‘emanating’ model to explain it. That is, they figure that an image is formed near the object when light irradiates it; and thus, the image is projected onto the screen and then the shadow is seen.

In this study, I design a series of activities about the concept of shadow formation according to the learning cycle model which consists of three sequential phases: Exploration, Concept Introduction and Concept Application, originally conceived by Robert Karplus in the 1960. There are several activities in each phase, and each activity is also arranged based on the learning cycle model.

In this study, I go a step further to analyze the geometrical optics misconceptions through historical documents and understand the conceptual developments of image formation, shadow formation, and ray concepts in scientific history. Based on this study, some instructional strategies of cognitive conflict can be developed, and adopted to physics instruction and curriculum design.