Physics KS3/4: John Tyndall and blue skies research

Professor Brian Cox recreates Tyndall's experiment, using a few drops of milk in a long tank of water.

Tyndall hypothesized that light was scattered by dust particles.

Blue light has a shorter wavelength and has a higher probability of being scattered, so the sides of the tank look blue and the red light penetrates to the far end of the tank.

Although we now know that individual molecules in the air, not dust particles, cause scattering, Tyndall's further exploration - leaving the dust for many days in a sealed box - allowed bacteria (as well as dust) to settle out of the water.

This provided significant support for the theory of microbes causing disease, which was still controversial at the time.

This short film is from the BBC series, Science Britannica.

Teacher Notes

This short film could be used to explain why the sky is blue and the sunset is red, and as an introduction to the concept of light waves, dispersion and scattering.

Students could be encouraged to replicate Tyndall’s experiment in class and review their understanding of the colour spectrum.

Students could discuss an aspect of nature that fascinates them and research experimental methods of learning about it.

Curriculum Notes

This short film will be relevant for teaching physics at KS3, GCSE/KS4 and National 4/5 and Higher.

The topics discussed will support OCR, Edexcel, AQA,WJEC GCSE in GCSE in England and Wales, CCEA GCSE in Northern Ireland and SQA National 4/5 and Higher in Scotland.

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