Many students struggle to understand that a light ray is (most often) just a model used to depict the behaviour of light

Light, Sound and Waves


Resources to Address This

  • Reflection of light  (5-11)

    Ref - SPT HS01 PN07

    When thinking about ray diagrams, it is important that you remember that they are a model: they predict what will happen, but do not show a photo-realistic imitation of the phenomenon.

    Sometimes it helps to start with all the light from a source and then reduce the diagram to a significant few rays.

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  • Ray diagrams model events  (11-14)

    Ref - SPT Li02 TL02

    The first point to make clear to pupils is that a ray diagram is a model of a real process and drawing one involves making various simplifications.

    Making these kinds of simplifications may seem obvious to the experienced teacher, but they are unlikely to be so obvious to pupils.

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  • Interpreting ray diagrams  (14-16)

    Ref - SPT Ra01 TL12

    A ray diagram is a tool used by physicists to explain or predict the behaviour of beams of light as they pass through objects such as glass blocks or lenses. 

    The distinction between real and theoretical worlds in relation to light is important. It is worth emphasising in your teaching:

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  • Experiments with a fan of rays (11-16)

    Ref - Practical Physics; Light and optics; Investigations with ray streaks

    Students should begin to realize that the light travels in straight lines and that an object is seen when light enters the eye. A lens bends light rays so that the rays pass through an image point. We think we see the object at the image point.

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The following studies have documented this misconception:

  • Grusche, S. () Students’ ideas about prismatic images: teaching experiments for an image-based approach. International Journal of Science Education,

    Review sheet

  • Muñoz-Franco, G.; María Criado, A. and García-Carmon, A. () Investigating Image Formation with a Camera Obscura: A Study in Initial Primary Science Teacher Education. Research in science education, Springer Science+Business Media B.V., part of Springer Nature 2018.

    Review sheet

  • Andersson, B. and Kärrqvist, C. () How Swedish pupils, aged 12‐15 years, understand light and its properties. European Journal of Science Education, 5 (4),


    DOI: 10.1080/0140528830050403.

    Review sheet

  • Watts, D M. () Student Conceptions of Light: A case study. Physics Education, 20,


    Review sheet

  • Osbourne, J.; Black, P.; Smith, M. and Meadows, J. () Primary SPACE project - light, Liverpool University Press.

    Review sheet

  • Ramadas, J. and Driver, R. () Aspects of secondary students' ideas about light, University of Leeds Centre for Studies in Science & Mathematics Education.

    Review sheet

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