KS4 Shine a ray of white light through a prism to reveal the spectrum of colours. Then repeat Newton's "crucial" experiment where he showed that once split into the spectrum the colours could be split no further. Take the red beam from the spectrum produced and shine that through another prism. Then ask your students to identify the seven colours in the spectrum.
Newton musically divided the spectrum, with colours corresponding to the notes of a scale. The violet end of the spectrum corresponds to the higher notes of the scale. Ask your students to think of another example of where musical harmonies were used as a model to understand the universe.