Many students in physics courses fail to achieve a desired conceptual change because they assign an incorrect ontology to the to-be-learned concept. This situation has been detected in previous research for the case of field lines: many college students assign material properties to the lines and describe them, for example, as tubes that contain or transport charges. The historical evolution of this concept shows that early scientists like Faraday assigned material properties to these lines in some occasions. In the present work a history-based instructional material was designed to foster the analysis of the ontology of field lines to help students at an Argentinean university achieve conceptual change. The predicates used by the students to describe physical situations were used as evidence of the assigned ontological status. Conceptual change was measured by the change in the proportion of geometrical predicates that students used when referring to the lines in a written questionnaire. This change was significantly higher for the students learning with the history-based material compared to those that learned in the regular class. Some characteristics of the material and geometrical ideas that students hold about the field lines were determined through an oral interview. ß

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Resumen. Se presenta un estudio de caso genérico (Merriam, 1998) que consta de dos partes. En la primera, se analiza la presentación de la corriente de desplazamiento en los textos de electromagnetismo de nivel universitario básico. El protocolo de análisis se elaboró desde el marco teórico de Alexander y Kulikowich (1994). Los resultados muestran que, en muchos textos: a) la traducción del sistema simbólico al lingüístico es escueta o imprecisa, b) la igualdad entre la corriente de desplazamiento y la de conducción se plantea sin aclarar su validez y c) algunos ejemplos plantean un campo eléctrico que varía linealmente con el tiempo, situación que no se estudia previamente en los libros de este nivel. La segunda parte analiza la comprensión que alumnos universitarios avanzados logran acerca de la corriente de desplazamiento a partir de los textos. Se concluye que existen graves deficiencias en la interpretación de las lecturas seleccionadas.Palabras clave. Corriente de desplazamiento, comprensión de textos, alumnos avanzados. Displacement Current: its presentation in textbooks and students̓ understanding of itSummary. A generic case study as that defined by (Merriam, 1998) is presented here. In the first part of the work, an analysis of how college-level textbooks address the concept of displacement current was carried out. The analysis was guided by Alexander's and Kulikowich's (1994). The results show that in most textbooks: a) the translation between the symbolic and the linguistic system is very limited or not sufficiently precise, b) when the equality between the Displacement Current and the Conduction Current is set, its validity is not stated, and c) some examples of work with an electric field that has a linear variation in time while this case has not been previously treated. The second part of this work deals with the understanding that college students acquire about Displacement Current from different textbooks. This work shows that serious deficiencies can be detected in their interpretation of the selected texts.

A generic case study as that defined by (Merriam, 1998) is presented here. In the first part of the work, the symbolic system used in basic electromagnetism books when presenting the concept of electric flux is compared with the symbolic system used in calculus books when presenting Gauss' Theorem. The analysis was guided by the Dual Coding Theory posed by Sadoski & Paivio (2004). The results show that, while there exists a great deal of uniformity within one area (Physics or Calculus), there exist discrepancies between areas. The second part of this work deals with the symbolic-symbolic translation that students are able to carry out when having learned Gauss Theorem with a symbolic system that is different from the one used in Physics. It is suggested that the lack of interpretation of what the symbols mean can initially contribute to hinder comprehension about the flux concept.