## Pupils generally do not intuitively recognise white light is a mixture of colours of light.

Light, Sound and Waves

Misconception

### Diagnostic Resources

The following worksheets may help to identify whether students hold this particular misconception.

• #### A spectrum of colours: the dispersion of light  (11-14)

Ref - SPT Li04 PN01

With the triangular block, the geometry of the prism is such that there is some separation of the different colours of light at the first face and then further separation at the second.

As a result the red light lands at a different point on the screen to the violet light and in between we can see the full spectrum of colours. The white light is dispersed into its constituent colours and the process is therefore referred to as dispersion.

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• #### A simple spectrum (11-16)

Ref - Practical Physics; Light and optics; Spectra and colour;

This should be as simple as possible, without complicated optics, as an introductory experiment.

The spectrum will be the most pure if the screen is held at the same optical distance from the lens as the image was before the prism was inserted, and the prism is turned to minimum deviation. However, turning the prism to a greater deviation will show a wider spectrum.

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## References

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, https://doi.org/10.1080/09500693.2017.1312625
• Haagen-Schützenhöfer, C. () Students’ conceptions on white light and implications for teaching and learning about colour. Physics Education, 52.
• Eaton, J., Anderson, C.W. and Smith, E.L. () Students' misconceptions interfere with learning: case studies of fifth-grade students. Research Series 128, The Institute for Research on Teaching, Michigan State University.