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Asia-Pacific Forum on Science Learning and Teaching, Volume 6, Issue 1, Article 1 (June, 2005) Peter HUBBER Explorations of Year 10 students’ conceptual change during instruction
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Asia-Pacific Forum on Science Learning and Teaching, Volume 6, Issue 1, Article 1 (June, 2005) Peter HUBBER Explorations of Year 10 students’ conceptual change during instruction
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Discussion of the findings
This study found geometrical optics to be a rich area for the prevalence of alternative conceptions among a group of Year 10 students. The occurrence of alternative conceptions is not surprising given the wealth of research studies with similar findings. Among the pre-instructional alternative conceptions there was evidence of students holding contradictory views in different contexts. For example, the understanding on the one hand of the belief that vision of an object in daylight conditions is only possible if it is illuminated while on the other hand vision is possible in nil light conditions. In another example, students had the view that a plane mirror image is located on the mirror surface midway between the object and observer. The students believed this view only applied to objects located directly in front of the mirror even though the application of the view could also apply to objects located to the side of the mirror.
While there was evidence of students holding contradictory views there was also evidence of alternative frameworks. However, the prevalence of alternative frameworks should not be judged according to whether the framework acts as an alternative to an existing scientific theory, across a similar domain, but should be judged by the consistency with which it is used across a limited domain. There was consistency in the alternative conceptions described as 'the only condition for vision of an object is for it to be illuminated', 'the extent of light propagation is dependent on the degree to which it can illuminate the area surrounding the luminous object', and 'the colour of an object is a property of that object'.
The teaching sequence proved successful in changing the understanding of the students in several of the key concept areas to a scientific one. Much of this success may be attributed to the adoption of constructivist-informed teaching and learning approaches. Such approaches, which involve addressing the extant knowledge of the students, may have been a significant factor in changing the students' understanding of geometrical optics. The success in changing the students' understandings of optics contrasts with those findings within the research literature that found students' conceptions resilient to change in the face of instruction. There was very little evidence of students reverting to pre-instructional thinking once they showed evidence of holding a scientific understanding. However, there was evidence of students' inability to apply their newly constructed scientific understanding to novel situations. For example, students had difficulty in applying the key concept relating to refraction in explaining the presence of the displaced image when an object was viewed through the side of a triangular prism.
In contrast to the success in changing the students' understanding of optics through the application of constructivist-informed teaching and learning strategies there were difficulties incurred by the students in achieving a scientific understanding of some key concepts. These concepts related to the emission of light from luminous objects, refraction, colour of objects and image formation in plane mirrors and convex lenses.
A possible factor in the persistence of the alternative conception that light is emitted in only one direction from each point on the luminous source was the lack of the teaching of the treatment of a luminous object as an aggregate of point sources rather than an integrated whole. From this treatment of a luminous object students should realise that each point on the source is emitting light in the same manner as individual point sources do so; that is, isotropically.
The problems associated with refraction lay with the students' inability to correctly predict the path light follows in passing from one transparent medium into another. The students tended to use the same rule for the predicted light path, which corresponded to light entering a transparent material from air, for different situations. There was no evidence of the students applying any of the teaching models presented as part of the teaching and learning sequence to predict the light path. This situation may have been the result of an 'induced incorrect generalisation' (Mohapatra, 1988) in the students' thinking caused by too much emphasis in the teaching sequence on drawing ray diagrams of light entering a flat transparent material from air. Therefore, instead of the students thinking about light changing speed in passing from one transparent material into another and applying a teaching model to predict the light path they have consistently applied the one rule that 'light bends towards the normal'.
The resilience of the alternative conception that colour is an intrinsic property of an object may have been due to the ease with which the scientific understanding of vision can be assimilated with this conception and the complexities of using a colour theory to explain the perceived colour of objects in different coloured lighting conditions. The perception of colour by the human eye is quite complex and is often in conflict with everyday language, which supports the alternative conception, and past experiences in art classes mixing paints and crayons. The assimilation of the alternative conception relating to colour with the vision concept may be quite natural for students if they are unaware of the concept that light is a mixture of different coloured light. From this perspective, the importance of possessing a prior understanding that light from the sun and other luminous objects, such as light bulbs, is composed of different coloured light would make it a key concept necessary to be understood before addressing the colour concept.
The lack of success in changing students' views about the emission of light presented a barrier to the scientific understanding of image formation process in mirrors and lenses. Another barrier to the image formation process in this research study was the students' understanding of a ray as a physical entity of light. This led students to progress from a holistic conceptualisation of an image travelling freely through space to a projected image conceptualisation of the image carried by rays acting like rails. Galili (1996) and, Galili, Bendall and Goldberg (1993) believe the projected image conceptualisation to be a well-defined intermediate state of knowledge of post-instructional students. The findings of this study support such a view given that each student passed through this conceptualisation before reaching a scientific understanding. Further research is needed to determine to what extent student thinking about the emission of light from luminous objects and ideas about the ray present a barrier to a scientific understanding of image formation and the construction of a projected image conceptualisation.
Copyright (C) 2005 HKIEd APFSLT. Volume 6, Issue 1, Article 1 (June, 2005). All Rights Reserved.
