Dispersion and colour sim
Shine a ray box through a glass prism to spread white light into a spectrum, slide colour filters into the beam, and light six coloured blocks with red, green or blue light to see which ones turn black.
Light: dispersion and colour · covers the IGCSE, GCSE topic
What the sim shows
White light is a mix of colours. Glass slows violet light more than red, so its refractive index is larger for violet and violet bends most: the prism spreads white light into a spectrum, red, orange, yellow, green, blue, indigo, violet. Red has the longest wavelength and lowest frequency; violet has the shortest wavelength and highest frequency. This is dispersion. The deviation D is the angle the ray is turned through by the prism. The prism is crown glass (BK7), with real refractive indices (1.5131 for red at 700 nm, 1.5296 for violet at 410 nm) and light meeting it at 50°, which turns red through 38.33° and violet through 39.78°. That difference is small, so the drawing spreads the colours 10 times wider than real; the readings are the real angles. A filter lets through only its own colour and absorbs the rest. An object looks the colour of the light it reflects: a red object reflects red and absorbs the rest, so under green or blue light it reflects nothing and looks black. The filters and blocks are ideal ones; real filters let through a band of colours.
- Filter holders: drag the ray box's carrier or the lamp's slide to choose white, red, green or blue
- Glass prism: white light spreads into a spectrum on the white screen
- Coloured blocks: each looks the colour of the light it reflects
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
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