Explorations of Year 10 students’ conceptual change during instruction

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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Description of study

This section has three parts which describe the (i) key concepts, (ii) teaching sequence, and (iii) data collection instruments.

Key concepts

The study implemented constructivist-informed teaching and learning approaches within a classroom setting in the topic of optics and documented any changes in the conceptual understanding students had about seven central concepts of geometrical optics (Table I) over a teaching sequence. The investigation was a classroom-based case study of a group of six students, within a class of 23 students. The teaching sequence consisted of three 47 minute lessons per week over a 9 week period.

Table I: Listing of Key Concepts of Optics

Number Descriptions of key concept

1. Light must enter the eye in a direction from the object before vision of that object is possible.

2. Light travels in straight lines until it hits something.

3. Each point on a luminous object emits light in all directions.

4.
(a)
When light is reflected from mirrored surfaces the rule of reflection holds true.

(b) Light reflects in all directions from a non-mirrored surface.

5. (a) In general, light will change direction when passing from one transparent material into another.

(b) Light will not change direction when passing from one transparent material into another if it hits the second material at right angles to its surface.

6. The colour of an object is the colour of the light that is reflected by the object.

7. (a) All the light from each point on an object that passes through a lens, or reflects off a mirror, contributes to the formation of a corresponding image point.

(b) The divergent light from each point on the object that passes through a lens, or is reflected from a mirror, either converges to the corresponding point on the real image or appears to diverge from the corresponding point on the virtual image.

Teaching sequence

At the beginning of the teaching sequence students were introduced to optics through the administration of a question sheet designed to elicit the concepts the students had about: (a) the direction of light from luminous sources to be able to see a non luminous object, (b) if vision is possible in the absence of light, and (c) if one could 'feel' a stare. The subsequent clarification and exchange of ideas through a class discussion led to further discussions following activities described as:

Student generated experiments to test if one could attract someone's attention through just staring at them. The experiments disconfirmed the alternative conception that through the act of staring something is emitted from the eye that will be detected by the person being stared at.

Students with alternative conceptions about vision in the absence of light were exposed to a disconfirming demonstration where they could experience the total absence of light in a photographic darkroom.

A 'senses' analogy was introduced to assist in the restructuring of concepts held about vision. In the analogy, something (for example, a sound, smell, or possibly light) activates a sense receptor, which then sends a message to the brain that interprets the message as a particular sense stimulus. This analogy was used to give plausibility to the key concept that light must enter the eye for vision to occur.

The students were given the opportunity to use their reconstructed concept of vision in a variety of situations throughout the teaching sequence. The application of the concept of 'the eye as a light detector' gave plausibility to other concepts addressed. For example, the concept of detection of light from an object is only possible through a straight section of pipe gave plausibility to the concept of rectilinear propagation of light. Also, the concept of the eye as a light detector was used to assist in the understanding of image formation in mirrors and lenses. The students were invited on many occasions throughout the teaching sequence to reflect on their original concepts of vision and how their concepts changed.

Teaching strategies were employed on a number of occasions where the explicit attempt was made by the teacher to promote conceptual conflict through the use of disconfirming, or 'surprise' demonstrations (Driver & Oldham, 1986), or a 'predict-observe-explain' (POE) technique (White & Gunstone, 1992). Some examples of the POE activities used were:

Several POE activities in relation to the students' understanding of shadows and pinhole images were modified from those developed in the Feher and Rice (1988) and Rice and Feher (1987) studies. Predictions were to be made as to the shape of images, or shadows, after changes were made to an aperture or obstacle shape that was placed between a light source and a screen in a darkened classroom.

A POE activity was developed from a disconfirming demonstration described by Singer (1979) to locate the position of the virtual image in plane mirrors. The disconfirming demonstration consisted of two candles on either side of a plane glass sheet with one of the candles lit. Through a parallax test, and direct observation, the alternative conceptions about the position of the virtual image were tested. As part of the POE technique the students were to predict the nature and the position of the virtual image with changes in the position of the observer as well as changes in the position of the lit candle. Another POE activity in relation to images in plane mirrors was used where students were to predict any changes to the image if the object, in this case a person, moved further away from a mirror.

A POE activity was developed from a probe of understanding used by Goldberg and McDermott (1987) about real images in converging lenses. From an initial arrangement of a luminous source, converging lens and a screen showing the real image, students were to make predictions about what would happen to the image if certain changes to the arrangement were made. For example, removing the lens completely or covering half of it or removing the screen.

Some further examples of disconfirming demonstrations that were employed include:

A red filter was placed in the path of blue light to disconfirm the alternative conception that the function of a filter is to dye, or change the colour, of the incident light after it passes through the filter.

A translucent screen was placed in a converging lens system (light source and lens) at the position of the real image but only covering half of the image. This demonstration, developed from one described by Conery (1983), disconfirmed the alternative conception that an aerial image is non-existent.

All the key concepts of the study (Table I) were addressed in the teaching sequence. However, time constraints imposed difficulties in providing the students sufficient time to fully explore their developing ideas about colour (key concept 6) and image formation in converging lenses (key concepts 3 and 7) in terms of applying new ideas to a variety of situations and reflection of how ideas were changed.

Data collection instruments

Multiple methods of collecting data, involving a range of qualitative and quantitative approaches, enabled triangulation to be used to support the internal validity of the study. The qualitative methods adopted included the researcher/teacher journal, which incorporated classroom observations, student workbooks, and three semi-structured interviews with each participating student of the study. The quantitative methods that were adopted included a questionnaire survey to determine the students' perceptions of the classroom environment that adopted a constructivist-informed approach to teaching and learning as well as classroom documentation that included tests, assignments, concept maps, worksheets and surveys. It should be noted that the focus of this article is on the conceptual change students have about concepts related to optics and so the data associated with the questionnaire survey to determine the students’ perceptions of the classroom environment is not provided. A full discussion of the data associated with this aspect of the study can be found in Hubber (2005).

The first two semi-structured interviews were designed to elicit the pre-instructional concepts held by the students in terms of the key concepts of the study. The first interview probed the conceptual understanding of the first three key concepts (see Table I) while the second interview probed the conceptual understanding of the last four key concepts (see Table I). The probes of understanding in the interviews generally took the form where some common stimulus, pictured in a diagram or presented physically, was initially presented to the student and then the student's interpretation of, or explanation for the stimulus, was sought without judgement as to the validity of the explanation (White & Gunstone, 1992).

In the first interview an example of the questions asked came from a Stead and Osborne (1980) study, which explored students' conceptions of light. The method of obtaining data was an 'interview-about-instances' technique (Osborne & Gilbert, 1980). The students were shown drawings on cards of instances of sources of light (for example, candle, television, heater, 'glow-in-the-dark' toy) both in daylight and night conditions, and reflectors of light (for example, moon, mirror, movie screen). Each student was shown the same sequence of cards and asked the same pair of questions for each card. The questions were:

1. Does the candle make light?

1a. (Why do you say that?)

2. What happens to the light the candle makes?

2a. (Does it stay around the candle or move out?)

2b. (About how far from the candle does the light from the candle go?)

Questions 1a, 2a and 2b were used, if needed, to elicit further information from the students. Other questions were modified and added where it was seen necessary to obtain a clearer understanding of the student's conceptions of luminosity and light propagation in daylight and night conditions.

In the second set of interviews the students' conceptions as they related to image formation in plane mirrors were explored using an approach used by Goldberg and McDermott (1986). The students were initially presented with a physical arrangement that involved a vertical rod placed in front of a plane mirror. The student and researcher were seated in front of the mirror in such a way that both could see an image of the rod; the student was seated to the right of the rod and the researcher was seated to the left. The student was provided with a diagram showing an overhead view of the arrangement of the mirror, rod, researcher and student. Some of the typical questions asked were, bearing in mind that, for some students, there was a modification of questions and follow-up questions in order to gain a clearer understanding of the student's conceptions:

Can you see an image of the rod in the mirror?

(Given an affirmative response from question 1). Where do you think the image actually is? Show me on the diagram.

If you were sitting where I am where do you think the image will be? Show me on the diagram.

The arrangement was now changed so that the mirror was covered and moved to the left of the student so that the mirror, rod and student were in the one line. With this arrangement, if the mirror was uncovered, the student would not be able to see the image of the rod but the researcher, who sat to the right of the student, could. The student was given an overhead diagram of the new arrangement and asked further questions, such as:

With this arrangement would you be able to see an image of the rod in the mirror now? (Given an affirmative response). Show me on the diagram.

Would I be able to see an image of the rod in the mirror? (Given an affirmative response). Show me on the diagram.

The third interview, conducted eight weeks after the teaching sequence, probed the conceptual understanding of all the key concepts of the study. Where the student had exposed an alternative conception either in the first two pre-instructional interviews or sometime during the teaching sequence supplementary questions were asked to probe for any change in conceptual understanding. Many of the questions were of the same type used in the tests administered during the teaching sequence. The students were presented with the questions in written form and many of the questions were accompanied with a diagram. The researcher verbally expressed each question, and if necessary, further explanation was provided. The students were expected to draw on the diagrams as well as provide verbal responses.

Copyright (C) 2005 HKIEd APFSLT. Volume 6, Issue 1, Article 1 (June, 2005). All Rights Reserved.

Number		Descriptions of key concept
1.		Light must enter the eye in a direction from the object before vision of that object is possible.
2.		Light travels in straight lines until it hits something.
3.		Each point on a luminous object emits light in all directions.
4.	(a)	When light is reflected from mirrored surfaces the rule of reflection holds true.
	(b)	Light reflects in all directions from a non-mirrored surface.
5.	(a)	In general, light will change direction when passing from one transparent material into another.
	(b)	Light will not change direction when passing from one transparent material into another if it hits the second material at right angles to its surface.
6.		The colour of an object is the colour of the light that is reflected by the object.
7.	(a)	All the light from each point on an object that passes through a lens, or reflects off a mirror, contributes to the formation of a corresponding image point.
	(b)	The divergent light from each point on the object that passes through a lens, or is reflected from a mirror, either converges to the corresponding point on the real image or appears to diverge from the corresponding point on the virtual image.