Student Descriptions of Refraction and Optical Fibers Fran Mateycik1, JJ Rivera1, DJ Wagner1,2, and Sybillyn Jennings3 1Rensselaer Polytechnic Institute, 2Grove City College, 3Russell Sage College Abstract: This poster reports our research into how students describe and think about optical fibers and the physical phenomena of refraction and total internal reflection (TIR) basic to their operation. The study was conducted as part of the improvement and expansion of web-based materials for an innovative Rensselaer introductory physics course1 which examines the physics underlying information technology. As we developed the prototype module, we examined students' understanding of the phenomena of refraction, TIR, and optical fibers through the use of clinical interviews. As students discussed refraction and tried to explain how optical fibers work, several patterns emerged. Our analysis of these patterns drives our assessment of the effectiveness of the revised materials in addressing students' transfer of learning as well as the development of a multiple-choice diagnostic tool. This paper presents our categorizations of student responses and discusses how we are modifying our materials to address these findings. 1Materials found at http://www.rpi.edu/dept/phys/ScIT/ Fiber Optic Network Optical Fiber next to sewing needle. The core of the fiber is 62 microns in diameter; the cladding is 125 microns. “quote” 1 “quote” 2 Laser light trapped in a plastic fiber. Air serves as the cladding. “quote” 3  Lillian C. McDermott, “Bridging the Gap Between Teaching and Learning: The Role of Research,” The Changing Role of Physics Departments in Modern Universities: Proceedings of ICUPE, ed. by E. F. Redish and J.S. Rigden.  E. Hunt and J. Minstrell, “A Cognitive Approach to the Teaching of Physics,” Classroom Lessons: Integrating Cognitive Theory and Classroom Practice, ed. by McGilly (MIT Press, 1994).  J. Piaget, The child’s conception of the world, trans. by J. & A. Tomlinson. (Littlefield, NJ, 1926/1972). RPI work supported in part by NSF CCLI Program under grant DUE-0089399. Thanks to Leo Schowalter for access to ScIT students, and to the rest of the ScIT advisory committee: Karen Cummings, Toh-Ming Lu, Saroj Nayak, Jim Napolitano, Peter Persans, and Wayne Roberge.