Field lines : hinge for the comprehension of field concept
Les lignes de champ : charnière pour la compréhension du concept de champ
Le Linee di campo : cardine per la comprensione del concetto di campo
Résumé
This thesis deals with the concept of a field, in particular magnetic and gravitational ones at two school levels: primary and secondary ones.
From the analysis of previous research and a deep content analysis, we focused this work on some specific hypothesis of research, based on two principal research questions: 1) can field lines representation facilitate a more global vision of the field (as opposed to the local one) and a differentiation of the different types of field by their maps; 2) can the differentiation of polar and dipolar fields allow students to identify the specific properties of the different types of field.
The research hypothesis are presented in two groups, one for each school level, and they are specified in sub-hypotheses, and put to the test. They are mostly related to the distinction between the two effects of magnetic interaction (attraction and orientation), to the conception of magnetic field lines as “lines of orientation” (and not lines of force), to the distinction between unipolar and dipolar field.
In two preliminary studies, at primary school, we identified some potentialities and difficulties of this approach at this school level. In particular: the source of magnetic field is more easily recognised by children than that of the gravitational field, in the magnetic interaction the attraction effect is dominant with respect to the rotation effect, and finally children are able to differentiate the shape of magnetic and gravitational fields, but they have some difficulties to pass from the difference between the shapes of field lines to the difference between the actions of the two sources.
On the basis of these two preliminary studies at primary school, we designed two teaching-learning sequences about magnetic field, at primary (9-10 years old) and secondary (18-19 years old) school levels.
At primary school level, field representation by field lines was accessible at a large part of the children. They where able to identify magnetic field lines with lines of orientation (and not of force) and to differentiate between the maps of the two fields (magnetic and gravitational), but we still observed the difficulty to pass from the difference between the maps to the difference between the actions of the two sources, whereas the obstacle “attraction is dominant”, found in the preliminary researches, seemed overcome.
At secondary school level, students used the shape of field lines to differentiate polar and dipolar fields. Field lines were used also to identify the analogies between fields. In this school context, the results of the analysis of the sequence and of the post test show to which extent – in fact: large - the approach proposed helps students consistently progress toward an understanding of the concept of a field. They also suggest guidelines for future research.
Ce travail de thèse se centre sur le concept de champ, en particulier sur les champs gravitationnel et magnétique et sur deux principales hypothèses de recherche : 1) la représentation des lignes de champ peut faciliter l'accès à une vision globale du champ (en rupture avec une vision locale dominante) et à une différenciation des divers champs par les formes des lignes; 2) la différenciation des champs polaires et dipolaires peut permettre d'identifier les propriétés spécifiques des divers types de champs. Deux enquêtes préliminaires au niveau de l'école primaire ont permis de développer des séquences d'enseignement concernant le champ magnétique à l'école primaire (9-10 ans) et secondaire (18-19 ans). A l'école primaire la représentation des deux champs à travers les lignes du champ est accessible à une bonne partie des enfants qui identifient les lignes de champ magnétique à des lignes d'orientation (et non "de force"), et différencient la forme des lignes de champ magnétique et gravitationnel mais ils ont des difficultés à retraduire cette différence de cartographie en terme de différence entre les actions des deux sources, tandis que l'obstacle "attraction dominante", relevé dans les études préliminaires, est largement surmonté. Au niveau de l'école secondaire, les élèves utilisent la forme des lignes des champs pour différentier les champs polaires et dipolaires. Les lignes de champ sont utilisées aussi pour identifier les analogies entre les champs. Les indications recueillies en cours de séquence comme lors d'un post test rendent crédible, dans ce contexte scolaire, l'adoption de l'approche proposée ici, et permettent d'orienter les recherches pour l'affiner.