A Learning Case Study in a Teaching Sequence in Geometrical Optics, using a Computer-based Model.
Christian BUTY - Septembre 2000

The studied domain of Physics is geometrical optics. The teaching sequence takes place in the last class of upper secondary school, in a normal class, during a eight-weeks-long lecture. The students use a computer-based representation of classical experiments. This representation obeys the laws of geometrical optics, by construction. It is a “ materialised model ”, first because it constitutes a physics model od the experiment, and secondly because it is a real entity with which the students can interact. They are thus expected to establish stronger links between the experimental field and the physics model.
We chose a case study methodology, grounded upon the complete recording of the verbal and gestural activity of one student. A semi-quantitative analysis of data aims to show the relation between the kind of resources the student uses, and his employment of physics theory. Our main result is that students, when they use the materialised model, express a larger diversity of kind of knowledge, than when they perform the experiments. Nevertheless, during the use of the computer, the link between what the students see on the screen and the experiments is not well realised, excepted when the teacher’s instructions ask it explicitly.
A qualitative analysis aims to investigate the construction of the concept of optical image par the observed student. The evolution of his conception can be described as a change in the force given to two aspects of the concept : the sharpness and the size. This analysis shows that the materiallised model can play the role of a “ milieu didactique ” for learning, under certain conditions mainly driven by the teacher’s intervention.