Physics · 3.2.5 Dispersion of light · Colour
Dispersion. Split it.
Shine white light through a glass prism and watch it split into the spectrum — red, orange, yellow, green, blue, indigo, violet. Violet bends most because it has the shortest wavelength and the highest refractive index. Try monochromatic light too.
0625 Topic 3.2.5 — Dispersion
Spectrum of white light
Monochromatic light
Variables
45
60
Refractive index by colour
Red (n ≈ 1.513)
deviates least
Violet (n ≈ 1.532)
deviates most
Why the colours separate
Glass has a slightly higher refractive index for shorter wavelengths, so violet bends more than red.
A second, inverted prism can recombine the spectrum back into white light.
📋 Method (Cambridge demonstration)
- In a darkened room, shine a narrow beam of white light at a triangular glass prism.
- The light refracts at both faces and emerges spread into a band of colours on a white screen.
- The order from least to most deviated: red, orange, yellow, green, blue, indigo, violet.
- Replace the white source with a single colour (monochromatic) — only one deviated beam appears, with no spreading.
Recombination: a second, inverted prism brings the colours back together into white light, showing white light is a mixture of colours.
🎯 Syllabus reference (0625)
- 3.2.5 Dispersion of light — describe the dispersion of white light by a glass prism; recall the seven colours of the visible spectrum in order; define monochromatic light; explain dispersion in terms of different refractive indices / speeds for different colours (wavelengths).