Light is a topic that exposes students to a fundamental aspect of science – different models are employed depending on the information one wishes to obtain about a physical system.
- The properties of visible light (~400 – 700 nm) examined through the activities are representative of electromagnetic waves (EM) in general.
- EM waves are transverse, which can be demonstrated through polarization.
- The ‘ray model’ can be used to understand the formation of shadows, reflection and refraction. This model simplifies the analysis of situations where the direction of light is altered.
- The ‘wave model’ can also be used to understand shadows, reflection, and refraction, but is required to understand phenomena such as polarization, diffraction and interference.
- Phenomena such as the decrease in measured intensity of light as a function of distance, or partial absorption/transmission through neutral density filters, are difficult to explain on the basis of the ‘ray model’. These can readily be explained by the ‘wave model’ as changes in the amplitude.
- The concept of energy is useful in explaining absorption/transmission, with the energy loss occurring as a result of the interaction of light with materials.
- It is the interaction with materials that result in reflection, refraction, shadows, polarization, absorption, and diffraction.
Science Education research has revealed a number of student misconceptions around the topic of Light:
- A recurring theme in studies is that light is said by students to illuminate objects and once ‘lit up’ these objects can then be seen. Students conceptualise light as a ‘local brightness’ and the act of seeing is often not considered to require that light travel directly to the eye.
- Students often ask questions of the form: ‘If I can see light and it travels as a ray, then why don’t I see bright rays crossing the room?’ This type of question demonstrates that, although students may accept that light is present in the space around them, they fail to understand the relationship between the image they see and the spatial-distribution of light in their environment (thereby altering their view of objects depending on their position).
- Students tend to classify light sources into those that are ‘natural’ and those that are ‘artificial’ and, accordingly, can attribute unique properties to the light produced in each case. Although the classification into ‘natural’ and ‘artificial’ sources is somewhat flawed (is a burning candle producing light through natural or artificial means?), it nevertheless demonstrates that students have actively attempted to distinguish between the properties of different light sources and the properties of the light produced. This can form the basis for a more scientific approach at classifying the optical properties of objects.
- Students tend to relate the reflection of light specifically to mirrors and ‘shiny surfaces’. They often fail to see the relevance of reflection in relation to the visible objects within their environment that are not ‘sources’ of light.
- Students often conceptualise that the image formed in a mirror is located on the surface of the mirror rather than behind it.
- Students often fail to understand the role of filters, even having studied the dispersion of white light by a prism. Many students consider that filters ‘alter the colour of light’ rather than allowing or preventing certain colours from passing through them.
Further reading:
‘Student Conceptions of Light: A Case Study’, D. M. Watts, Phys. Educ. 20, 183 (1985)
‘Exploring Students’ Concepts of Light’, B. F. Stead and R. J. Osborne, Australian Science Teacher’s Journal 26(3), 84 (1980)
‘Student Misconceptions about Light in Algeria’, D. Blizak, F. Chafiqi, and D. Kendil, http://spie.org/etop/2009/etop2009_4.7.35.pdf (Proceedings of the 2009 Conference on Education and Training in Optics and Photonics).
SPIE is the International Society for Optics and Photonics (www.spie.org) and maintains many excellent resources and tools for teachers and educators.
With regard to the features of an inquiry approach, teachers especially need to gain pedagogical content knowledge enabling them to “engage students in asking and answering scientific questions, designing and conducting investigations, collecting and analyzing data, developing explanations based on evidence, and communicating and justifying findings”. This mainly involves teachers being able to:
- Provide questions to frame unit and questions for discussion
- Suggest approaches for using technology as laboratory and cognitive tools.
- Suggest approaches for collecting and analysing data.
- Support students in designing their own investigations.
- Suggest approaches to help students construct explanations based on Evidence
- Provide approaches for communicating science knowledge.