In this study, it was tried to explore mental models of light utilized by the Turkish students for the explanations of single-slit diffraction and double-slit interference of light. This research has been carried on the group of 294 students made up of 175 introductory and 119 advanced level students studying in the departments of engineering, physics and physics teachers at a Turkish University. Open - ended questions pertaining drawings and explanations were used as data collection tool. As a result of quantitative and qualitative analysis, three mental models which were named as wave, ray and particle being used by the students while explaining these subjects, were described. Serious difficulties were observed towards the usage of these models for the both levels of the student groups and some differences were indicated between the introductory and advanced level university students in terms of usage of these models.
In general, the results of this research indicate that the students in both level while trying to explain the phenomena of interference and diffraction of light have developed very different mental models of light and in order to explain the phenomena they haven’t got a functional wave model. This situation would prevent them to sense the nature of wave of the matter (Steinberg et al., 1996; Vokos et al., 2000). Students’ mental model changes serve as the most important source covering learning processes and conceptual changes of them (Park 2006). For this reason, it is required to revise the fundamental optics teaching in order to realize the students to learn the light models effectively.
Although interference and diffraction phenomena have continuously been explained in terms of the wave model of light both at university and high school as well as in the source books, because during the explanations of these topics, rays have been used continuously without realizing that these would be just geometrical representations, these results are naturally not unexpected situation. This shortage appearing very simple pushes students to very mistakes with respect the conception of light and wave model. Several studies (Galili 1996; Galili & Hazan 2000) have shown that many difficulties may occur when using the ray model of light in teaching. Spherical wave surfaces should be used instead of light beams or sinusoidal waves to describe light propagation from source. Also, the wave fronts between slit(s) and pattern should be drawn and the interference should be shown while teaching the interference and diffraction subjects. This usage would prevent students from thinking geometrical optic laws in the physical optics subjects. Also, the water waves in ripple tank would be useful to describe the wave surface as a model for the light wave.
However, the educators should investigate students’ understanding level about the light models in their optics instruction. In addition, they should use the proper instructional materials to overcome the alternative ideas of the students. It is hoped that the results of this study will help the educatiors to recognize the students’ difficulties in both introductory and advanced levels. Besides, the studies about how students use the light models for explaining the other subjects in optics should be conducted.