EDUCATION Revista Mexicana de F´ ısica E 17 (2) 215–225 JULY–DECEMBER 2020 Learning about wave optics: the effects of combining external visualizations with extreme case reasoning A. Vidak Faculty of Chemical Engineering and Technology University of Zagreb, Croatia, Savska cesta 16, 1000 Zagreb, tel: ++385 1 4597 106, e-mail: avidak@fkit.hr V. Danani´ c Faculty of Chemical Engineering and Technology University of Zagreb, Croatia Savska cesta 16, 1000 Zagreb, tel: ++385 1 4597 107, e-mail: vdanan@fkit.hr V. Meˇ si´ c Faculty of Science, University of Sarajevo, Bosnia and Herzegovina Zmaja od Bosne 33-35, 71000 Sarajevo, tel:++387 33 27 98 68, e-mail: vanes.mesic@gmail.com Received 8 April 2020; accepted 22 May 2020 In this study, we investigated whether combining external visualizations with extreme case reasoning may the development of a conceptual understanding of wave optics. For purposes of answering our research question, we conducted a pretest-posttest quasi-experiment, which included 179 students from a first-year introductory physics course at the University of Zagreb, Croatia. Students who were guided through extreme case reasoning in their wave optics seminars significantly outperformed their peers who received conventional teaching treatment. Findings from our study suggest that combining external visualizations with extreme case reasoning facilitates the development of visually rich internal representations, which are a good basis for performing mental simulations about wave optics phenomena. Besides, it has been also found that many students use the “closer to the source implicates greater effect” p-prim when reasoning about certain relationships, such as the relationship between fringes’ dimension and slits-screen separation. Keywords: Wave optics; extreme case reasoning; p-prims; misconceptions. PACS: 42.25.-p DOI: https://doi.org/10.31349/RevMexFisE.17.215 1. Introduction Wave optics has many applications in the field of lasers, mi- crocomputers and electronic detectors. We can say that its ap- plications extend to all areas of modern science, engineering, and technology [1]. In everyday life, wave optics is useful to understand some phenomena, such as interference of light on peacock feathers and colored appearance of a soap bub- ble [2]. Generally, wave optics significantly contributes to learning one of the most important physics concepts, which is the wave concept. Consequently, learning wave optics is very important for conceptual understanding of other areas of physics, e.g., solid-state physics and quantum mechan- ics [3,4]. However, many students struggle with developing a basic understanding of wave optics [5–7]. Earlier studies have shown that students often do not understand whether they should use geometric or wave optics to solve standard textbook problems related to light phenomena [4,8]. Under- standing of wave optics requires simultaneous thinking about spatial and temporal aspects of wave motion. However, re- search showed that human working memory is highly lim- ited [9]. That is why thinking about wave phenomena induces high cognitive load [10]. Furthermore, reasoning about wave optics is additionally obstructed by the fact that students lack intuitive mental models about wave optics [11]. For developing a deep understanding of wave optics, stu- dents have to go far beyond intuition. Actually, examples from the history of physics show that deeper truth is often hidden under the surface of everyday experience. In many cases throughout history, scientists discovered this truth by using analogies and extreme reasoning [12,13]. Stephens and Clement stress that extreme case reasoning is at work when, ”in order to facilitate reasoning about a situation A (the tar- get), a situation E (extreme case) is suggested, in which some aspect of situation A has been maximized or minimized” [14]. For example, it seems that Galileo Galilei used extreme case reasoning for mentally simulating what would happen to the motion of a sphere moving between two smooth inclined planes facing each other. He concluded that as the angle of the second plane tends to zero, the distance covered by the sphere tends to infinity [15].