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3.5.2Stoichiometry

Dispersion — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 4 parts Lesson 8 of 28 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 4Refraction by Colour

3.5.2 Dispersion
White light
  • White light is a mixture of all the visible colours, each with its own frequency and wavelength.
Different amounts
  • Each colour is refracted by a different amount as it enters and leaves the glass prism.
Violet
  • Violet light has the shortest visible wavelength and is refracted the most by the prism.
Red
  • Red light has the longest visible wavelength and is refracted the least, so it lies at the edge of the spectrum furthest from violet.
Dispersion
  • The separation of white light into its component colours is called dispersion.

Part 2 of 4Forming a Spectrum with a Prism

1
A narrow beam of white light is directed at one face of a triangular glass prism.
2
On entering the glass the light refracts towards the normal, and each colour bends by a different amount.
3
On leaving the prism each colour refracts away from the normal, which spreads the beam further.
4
The colours emerge as a band from red to violet, which can be projected onto a screen.

Part 3 of 4Colour Order and Rainbows

Colour Order and Rainbows
Red
  • Red has the longest wavelength of visible light and therefore the lowest frequency.
Indigo and violet
  • Indigo lies between blue and violet, and violet has the shortest visible wavelength and highest frequency.
Rainbows
  • Raindrops refract, reflect and disperse sunlight, producing a rainbow when the Sun is behind the observer.
Speed in glass
  • Each colour travels at a slightly different speed in glass, and this difference causes the spread into a spectrum.

Part 4 of 4Exam Checklist & Tips

3.5.2 – Key Points for the Exam

  • Dispersion The splitting of white light into its component colours, because each colour is refracted by a different amount.
  • Spectrum The ordered band of colours produced when white light is dispersed.
  • Prism A transparent block with flat faces, used to disperse light.
  • Refraction The change in direction of light caused by a change in its speed at a boundary.
  • Wavelength The length of one complete wave, which determines the colour of visible light.

Common Mistakes

  • Saying the prism changes the colour of the light.
  • Saying violet light is refracted least, when it is refracted most.
  • Claiming that different colours travel at different speeds in a vacuum, when they do not.

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