Coherence of light and interference : students’ reasoning and historical difficulties

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Laurence Maurines

Université Paris-Sud 11, DidaScO, batiment 333, 91405 Orsay cedex, France

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This research examines the difficulties raised by the learning of light interference. Focused on interference of two waves and on the conditions for their production, it concerns three interferential devices (Young’s holes, Fresnel’s mirrors, thin plates) and two types of light (totally or partially coherent). Analyses of the physics of light interference, of its history, of its presentation in university books, and of the studies on conceptions on waves, have been made. Fifteen questionnaires were elaborated. 758 French and Tunisian students (aged 19-23) were questioned after teaching. Several tendencies of reasoning, which are linked together, are put forward. Two are encountered across different domains of physics: focusing on perceptive aspects, diminishing the number of physical quantities that have to be considered. One concerns the difficulties raised by the interpretation of diagrams with parallel rays in optics. Another one is closed to the tendency revealed for diffraction situations: students do not use the wave superposition principle and the interferential device seems modulate the amplitude of the incident wave. The last ones are specific to interference and concern the conditions for their production: for students, it is sufficient to have two point sources or it is necessary to have two monochromatic waves in phase. This research leads to some pedagogical suggestions: to draw diagrams with rays and waves surfaces when explaining the formation of images in order to emphasise that geometrical optics is a particular model derived from the wave theory of light, to reduce all interference situations to the prototypical situation with two sources, to precise the conditions for interference at the beginning of the first lesson

Key Words:University, conceptions, history of optics, light interference, coherence


  • Romdhane I. & Maurines L. (2003) "Students and the interference of light : first results".Proceedings of the fourth international conference of ESERA, Noordwijkerhout, on web:
  • Romdhane I. § Maurines L. (2005) Coherence of light and interference: historical ideas and students’ difficulties. Proceedings of the fifth international conference of ESERA, Barcelone, p. 25, on cd-rom

Correspondence :

Intissar Romdhane

Lycée secondaire de Khniss-5011 Khniss- Tunisie

Tél : +21698965084

Fax : +21673535586

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