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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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Findings
Each of the six case study students had several alternative conceptions as they related to seven key concepts of geometrical optics. There were alternative conceptions in each of the key concept areas that reflected pre-instructional ideas as well as alternative conceptions generated during the teaching sequence. Another finding that was found during and following the teaching sequence was related to the students’ understanding of the nature of light. Each student on several occasions expressed the alternative conception that light actually consists of rays.
The following tables describe the alternative conceptions held by each student with respect to the key concept areas prior to the teaching sequence as well as those alternative conceptions present eight weeks following the teaching sequence. Each student has been given a pseudonym. One of the students, Christine, held a greater number of post-instructional alternative conceptions than the rest of the students. A possible reason may have been Christine’s irregular attendances to class; she did not attend seven classes spread out over the teaching sequence.
Table II: Alan's Alternative Conceptions before and following the Teaching Sequence
Light from dim luminous objects does not travel very far from the object. Each point on a luminous object emits light in one direction. Each point on a luminous object emits light in one direction. The reflection rule does not hold true for curved mirrors. The reflection rule is violated in explaining that the image of an object in front of a plane mirror is on the mirror. Light bends towards the normal when it passes from a transparent material into air. Light bends towards the normal when it passes from a transparent material into air.
Light can change direction when perpendicularly incident to an air/material interface.
Objects have coloured components that change the colour of the incident light.
The function of a filter is to change the colour of the transmitted light.
The image of an object in front of a plane mirror is directly in front of the object and on the mirror surface.
An object that is not directly in front of a plane mirror has its image on the surface of the mirror in a position midway between the object and the observer.
The process of real image formation in a convex lens is similar to pinhole image formation where the lens replaces the pinhole. Each object point emits a single ray that carries all the structural information about the corresponding image point.
The reflected light from a plane mirror carries the image to the observer’s eye. While Alan showed evidence of holding pre-instructional alternative conceptions in several of the key concept areas he did have a scientific view of the vision process and specular and diffuse reflection of light. In terms of image formation in lenses Alan understood the process as one similar to that of pinhole image formation. He appeared to have constructed a view that each point on the object emits a single ray that carries all the structural information about the corresponding image point.
After the application of teaching strategies that directly addressed the alternative conceptions that were elicited, many of Alan's pre-instructional alternative conceptions were no longer apparent. The newly constructed scientific conceptions were still evident in the third interview that occurred two months after the Year 10 teaching stage. However, as Table II shows, there still remained alternative conceptions. Alan's inconsistency in predicting directional changes of light in explaining refraction effects may stem from an inability to consistently apply any of the teaching models taught in the teaching stage to predict the path of light through transparent materials. Alan's explanations of image formation in lenses were consistent with the key concept. However, he continued his thinking about light rays carrying the image information in his explanations of image formation in plane mirrors. Such a view is described by Galili, Bendall and Goldberg (1993) as a ‘projected image conceptualisation’.
Table III: Beth's Alternative Conceptions before and following the Teaching Sequence
Light only needs to illuminate an object before vision of that object is possible.
Humans can see in the total absence of light after spending some time in dark conditions.
Nocturnal animals can see in the total absence of light.
Light from a luminous object travels only as far as it can illuminate the area surrounding the luminous object.
Light from a bright luminous source will travel further than a dim luminous source and light travels further at night than during the day.
Each point on a luminous object emits light in one direction. Each point on a luminous object emits light in one direction. Light may change direction within a transparent material through reflecting on particles within the material. The colour of an object is a physical property of that object.
The function of a filter is to change the colour of the transmitted light.
The colour of the reflected light from an object is a mixture of the incident light and colour of the object itself. The image of an object in front of a plane mirror is the same distance behind the mirror as the object is in front of the mirror and its position is midway between the object and the observer.
An object that is not directly in front of a plane mirror has no image for any observer.
In a convex lens system the real image is formed at the object then travels through space where it gets inverted by a lens and is finally captured by a screen where it may be observed.
In a convex lens system the real image is formed at a lens then travels through space until captured by a screen where it may be observed. Beth showed evidence of holding pre-instructional alternative conceptions in several of the key concept areas. There was some evidence of alternative frameworks as coherent views where Beth linked her understanding of the vision process with the extent of light propagation from luminous sources. Her understanding of coloured objects was consistent with this linkage. However, there was also evidence of contextualised thinking such as vision in nil light conditions and the non-existence of a plane mirror image for an object placed to the side of the mirror. A holistic conceptualisation (Galili, Bendall & Goldberg, 1993), where the image is created at the object and travels through space, dominated Beth's pre-instructional thinking about the image formation process in a convex lens.
Throughout the teaching stage of the study there was significant growth in understanding with some retention of alternative conceptions. There remained evidence of a framework of understanding involving vision, extent of light propagation from luminous sources and coloured objects. Beth used her newly constructed scientific understanding of vision (key concept 1) to explain the extent of light propagation from luminous objects (key concept 2). In terms of her thinking about coloured objects Beth incorporated her scientific understanding of vision into her pre-instructional alternative conception. Beth's understanding of image formation in convex lenses become more analytical but still retained aspects of a holistic conceptualisation. Her thinking is characterised as a projected image conceptualisation (Galili, Bendall & Goldberg, 1993) where the image is carried by light rays acting like rails.
Table IV: Christine's Alternative Conceptions before and following the Teaching Sequence
Light only needs to illuminate an object for vision of that object to occur. The image of an object in front of a plane mirror is on the mirror surface in a position midway between the object and the observer. The extent of light propagation from a luminous object depends on the brightness of the object. Light from a dim object stays around the object whereas light from a bright object travels some metres before fading away. Light from luminous objects fades away with distance from the source. Each point on a luminous object emits light in one direction. Each point on a luminous object emits light in one direction. Light reflects off non-mirrored surfaces specularly. Light bends towards the normal when it passes from a transparent material into air.
Light can change direction when perpendicularly incident to an air/material interface.
The function of a filter is to change the colour of the transmitted light. The colour of the reflected light from an object is a mixture of the colour of the incident light and the inherent colour of the object. The image of an object in front of a plane mirror is directly in front of the object and on the mirror surface.
An object that is not directly in front of a plane mirror has no image for any observer.
In a convex lens system the real image is formed at a lens then travels through space until captured by a screen where it may be seen.
The image of an object in front of a plane mirror is on the mirror surface in a position midway between the object and the observer.
The reflected light from plane mirrors carries the image to the observer’s eye.
Ina convex lens systems the real image is formed at the lens then travels through space until captured by a screen where it may be seen.
Before the teaching of the key concepts of geometrical optics Christine showed evidence of holding alternative conceptions in several of the key concept areas. Unlike Alan and Beth she had not developed firm views about what gives colour to an object or an explanation for refraction effects. In understanding real image formation in convex lenses there was a holistic conceptualisation of an image moving through space. This holistic conceptualisation was consistent with Christine’s understanding that the image in a plane mirror is directly in front of the object on the mirror surface.
Many of the pre-instructional alternative conceptions were retained despite the adoption of teaching strategies to directly address them. This result was contrary to each of the other students and may be due, in part, to Christine's reported absences from her Year 10 studies. However, Christine did gain a scientific understanding of the vision process. This understanding was reflected in her alternative conceptions of the colour of objects, as Beth had done, and the placement of the image in a plane mirror. Christine had maintained her holistic conceptualisation of the real image formation process in a convex lens.
Table V: Danielle's Alternative Conceptions before and following the Teaching Sequence
Nocturnal animals and humans can see in the absence of light.
Light only needs to illuminate an object for vision of that objet to occur.
The extent of light propagation from a luminous object depends on the brightness of the object. Light from a dim object stays around the object whereas light from a bright object travels some distance away.
Light can bend around clouds.
Each point on a luminous object emits light in one direction. An inability to apply key concept 5 to explain a novel refraction phenomenon. The colour of an object is an inherent property of the object.
The function of a filter is to change the colour of the transmitted light.
The colour of an object is determined by what coloured light it absorbs. The image of an object in front of a plane mirror is directly in front of the object and on the mirror surface. An object that is not directly in front of a plane mirror has no image for any observer.
In a convex lens system the real image is formed at the object then travels through space where it gets inverted by a lens and is finally captured by a screen where it may be seen.
The reflected light from a plane mirror carries the image to the observer’s eye.
The production of part of the real image formed by a convex lens is affected by obscuring part of the convex lens.
Danielle showed evidence of holding alternative conceptions in several of the key concept areas. Danielle's pre-instructional thinking was very similar in a number of ways to Beth. For example, the contextualised thinking of the ability to see in nil light conditions. Also, the coherence in thinking between vision of objects in light conditions with the extent of light propagation from luminous sources and colour of objects, thus suggesting a possible alternative framework. Danielle also showed evidence of a holistic conceptualisation for image formation in lenses. Like Christine, Danielle had limited views on refraction.
Throughout the teaching stage there was significant growth in understanding with some retention of alternative conceptions. There was now evidence of a framework of scientific understanding involving vision and extent of light propagation from luminous sources. Although this framework was consistent with Danielle's view of coloured objects there was confusion as to what coloured light gets reflected from the object. As with Beth and Christine, Danielle's thinking about image formation in a lens and plane mirror was one of a projected image conceptualisation (Galili, Bendall & Goldberg, 1993).
Table VI: Evan's Alternative Conceptions before and following the Teaching Sequence
Light from dim luminous objects only travels metres whereas light from brighter objects travel further.
Light travels from luminous objects in waveforms.
Each point on a luminous object emits light in one direction. Each point on a luminous object emits light in one direction. Non-mirrored surfaces reflect light specularly. Light leaving a transparent material into air bends towards the normal. The function of a filter is to change the colour of the transmitted light. The image of an object in front of a plane mirror is on the mirror surface in a position midway between the object and the observer.
The image of an object placed to the side of a plane mirror does not exist for any observer.
In a convex lens system the real image is formed at the object then travels through space where it gets inverted by a lens and is finally captured by a screen where it may be seen.
Evan showed evidence of holding pre-instructional alternative conceptions in several of the key concept areas. However, he, like Alan, did have a scientific view of the vision process. Evan did not offer any views as to the phenomena of refraction or coloured objects. In terms of image formation in a convex lens he was analytical to some degree connecting the change in light direction with image formation. This thinking supports a projected image conceptualisation (Galili, Bendall & Goldberg, 1993). Like Beth, Evan showed contextualised thinking in terms the absence of an image when an object is placed to the side of a plane mirror.
During the teaching stage there was significant growth in understanding with some retention of alternative conceptions. The retention of the alternative conception that 'each point on a luminous source emits light in one direction' is consistent with each of the other students except Frank. The prevalence of the view that light deviation is towards the normal may suggest that Evan applied a general rule rather than considering if the light speeds up or slows down and applying a teaching model to determine the light direction.
Table VII: Frank's Alternative Conceptions before and following the Teaching Sequence
Light only needs to illuminate an object for vision of that object to occur. Cats can see in nil light conditions. Light from luminous objects only travels as far as they are visible. Each point on a luminous object emits light in one direction. Non-mirrored surfaces reflect light specularly. The change in direction when light passes from one transparent material into another is due to the reflection of light. The change in direction when light passes from one transparent material into another is not always correctly predicted. The colour of the reflected light from an object is obtained from the object.
The function of a filter is to change the colour of the transmitted light.
The image of an object placed to the side of a plane mirror is in a position that is behind the mirror and can be seen by an observer on the same side of the mirror as the object.
In a convex lens system the real image is formed at the object then travels through space where it gets inverted by a lens and is finally captured by a screen where it may be seen.
The reflected light from a plane mirror carries the image to the observer’s eye. The real image formed by a convex lens is created by the perpendicularly incident light on the lens from the object. The image is created at the lens and keeps travelling until captured by a screen where it may be screen. Before the teaching of the key concepts of geometrical optics Frank showed evidence of holding alternative conceptions in several of the key concepts. As with Beth and Danielle there was evidence of coherence in thinking about vision of objects in light conditions with the extent of light propagation from luminous sources and colour of objects, thus suggesting a possible alternative framework. Also common to Beth and Danielle, as well as Christine, was evidence of a holistic conceptualisation (Galili, Bendall & Goldberg, 1993) of real image formation in a convex lens.
Many of the pre-instructional alternative conceptions were no longer apparent following the Year 10 teaching stage suggesting significant growth in understanding. The alternative framework suggested in pre-instructional thinking was now a framework of scientific ideas. However, there still remained some alternative conceptions. The persistence of difficulties Frank had with changes in light direction in refraction effects was common to other students as was a projected image conceptualisation (Galili, Bendall & Goldberg, 1993) for image formation in convex lenses.
Copyright (C) 2005 HKIEd APFSLT. Volume 6, Issue 1, Article 1 (June, 2005). All Rights Reserved.
