The ‘thin lens’ in the light of idealisations

Abstract

This paper argues that the simplifying idealisations assumed in making complex science tractable should be identified and discussed before model-building. It is suggested that alternative conceptions can persist, and learning difficulties arise for students when they do not adequately understand these idealisations. We argue that explicitly addressing idealisations for a particular physical phenomenon can ease students’ conceptual understanding. A theoretical framework for identifying and reflecting idealisations is introduced based on epistemological considerations from science philosophy. The thin lens approximation of geometric optics, a common topic taught in the introductory classroom, is used as an archetypal illustration.