This thesis investigates the cognitive resources that pupils engineers in a PBL (Problem based Learning) in a task of conception of a technical object mobilize. The situation-problem with which these pupils are confronted is constituted by an unpublished technical system of refrigeration without outside contribution of energy. In this learning, the pupils have to conceive the technical object and learn concepts in thermodynamics. Two groups of pupils are compared: the first one has an analogical model of a situation known to approach the new situation; the second has only the text. The questions of researches: what build these pupils as knowledge? What bring these two types of learning (the learning by a known situation and the learning by the text)? What are the obstacles which meet these pupils? The hypotheses: a learning by a known situation leads to the construction of operational knowledge (concepts tools). A learning by the text leads to the construction of knowledge out of context (concepts objects). A learning by the situations in a didactic device leads later to the construction of category-specific concepts. These two types of learning involve the epistemological obstacle in the construction of the concepts in them two functions: tool and object.
