Dec 13 – 16, 2021
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The Simplicity-Completeness Issue In Physics Explanations Discussing The Rainbow With Student Teachers

Dec 13, 2021, 11:00 AM
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Presentations in Wroclaw 9. Initial teacher education, teacher professional development and Technological Pedagogical Content Knowledge Parallel 1 - Wroclaw


Prof. Laurence Viennot (University of Paris)


The Simplicity-Completeness Issue In Physics Explanations
Discussing The Rainbow With Student Teachers

Laurence Viennot
Matter and Complex Systems UMR7057 University of Paris

Abstract. This study explores the extent to which student teachers (STs) of physics can detect consequential gaps in a given explanation (RQ1), and the extent to which they sacrifice simplicity for completeness when designing an explanation for a given audience (RQ2). A very limited explanation of the primary rainbow (“one ray”) was discussed with 33 STs, using two successive questionnaires. The STs were often unaware that the “one ray” explanation was deeply incomplete (RQ1), and the dilemma between simplicity and completeness often remained unresolved after a critique of the explanation’s incompleteness (RQ2). The implications for teacher preparation are finally discussed.

1 Introduction
This paper adresses Shulman’s questions [1] ‘Where do teachers' explanations come from? How do teachers decide what to teach, how to represent it?’ (p. 8). To articulate the strengths and weaknesses of an explanatory text, it has recently been proposed [2] to use grids based on explicit criteria. The present study focuses on the criterion of completeness and two other criteria that may seem a priori incompatible (simplicity) or congruent (coherence). Focusing on these criteria, the study investigates the extent to which student teachers (STs) detect consequential gaps in a given explanation, and how this influences their decision-making process. The chosen topic (the rainbow) was limited to the case of the primary rainbow.

2 Previous research, rationale, and research questions
How STs make decisions about explanations that they will use in teaching a given audience can be understood as a two-step process: a critical analysis of explanations commonly applied to the topic in question and a decision based on the perceived benefits and risks of each candidate explanation [3]. It is common to observe a conflict between completeness and simplicity. In the present study, the participating STs were introduced to critical analysis as the detection of gaps in an extremely limited explanation of the primary rainbow. Particular attention was paid to one of these shortcomings, which consists in considering only one particular incidence of a solar ray on a drop to explain the value of its deflection ("one-beam" explanation). Such an explanation is logically invalid since another incident ray - for example a diametrical ray - would lead to a different deflection - if any at all. The two research questions are: (RQ1) To what extent do STs recognise the gaps in this incomplete explanation?; (RQ2) Do participants consider it necessary to provide an explanation that is more coherent and less simple—in this case, for first-year university students—and why?

3 Experimental design
The participants were 33 student teachers (STs) at the end of a master's degree preparing for teaching physics and chemistry. A first questionnaire (Quest. 1) explored what additional explanations they thought first-year university students would need beyond the “one ray” explanation. Sent after the first questionnaires were returned Quest., 2 begins by explaining that the specific incidence considered in the “one ray” explanation corresponds to a maximum brightness of the reflected beam. Participants were then asked what value they assigned to the explanation of this point to ensure a good understanding of the rainbow in the target audience. The comments in response to Quest. 1 and 2 were grouped on the basis of a thematic analysis.

4 Main results and discussion
Only one participant (out of 33) explicitly pointed out the logical incompleteness of the “one ray” explanation, while many other complementary explanations were requested. This clearly indicates that the issue of logical incompleteness is hardly detected in this group even though it invalidates the explanation. With regard to the value of completing the “one ray” explanation as proposed in Quest. 2, almost all respondants declared that it was important, but several comments expressed ambiguous positions such as “So the diagram is still right, it simply omits (for simplicity) the infinite number of rays that are diffracted” and several hints suggest that the simplicity-coherence dilemma was not easily resolved. This research indicates that STs would benefit greatly from a frequent practice of critical multi-criteria diagnoses and explicit consideration of the interrelated issues of simplicity, consistency and completeness. Further research is needed to optimise teacher preparation in this regard.”


[1] L.S. Shulman, Those who understand: Knowledge growth in teaching, Educational researcher, 15(2) (1986) 4-14.
[2] L.Viennot and N. Décamp, Developing Critical Thinking in Physics The Apprenticeship of Critique, (Contributions From Science Education Research, vol. 7) (Berlin: Springer) (2020)
[3] L. Viennot Incomplete Explanations in Physics Teaching Discussing The Rainbow With Students Teachers, Eur.J. Phys. (2021) ⟨10.1088/1361-6404/ac1500⟩

Primary author

Prof. Laurence Viennot (University of Paris)

Presentation materials