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8.4Physics 02. Light And Sound

Know that white light is made of many colours and this can be shown… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 4 of 5 1 quiz

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Lesson summary

8.4 White light and the spectrum: dispersion by a prism — CHECKPOINT - Lower Secondary Science 0893 notes: Know that white light is made of many colours and that this can be shown by dispersion with a prism.White light — light that is made up of a mixture of different colours.New…

  • Order of colours
  • Number of colours
  • Different angles
  • Conditions for seeing a rainbow
  • Refraction
  • Newton — in 1666 Isaac Newton showed that white light could be split into colours using a triangular glass prism

Part 1 of 6White light

White light
  • White light light that is made up of a mixture of different colours.
Newton
  • Newton in 1666 Isaac Newton showed that white light could be split into colours using a triangular glass prism.

Part 2 of 6The spectrum

Spectrum
  • Spectrum the range of colours in white light.
  • The colours merge from one into the next.
Order of colours
  • Order of colours red, orange, yellow, green, blue, indigo and violet.
  • The name ROY G. BIV helps to remember the order.
Number of colours
  • Number of colours most people agree on seven, but some see five or six.

Part 3 of 6Dispersion

Dispersion
  • Dispersion the splitting of white light into different colours.
Cause
  • Cause dispersion happens because light is refracted by the prism.
Different angles
  • Different angles each colour is refracted through a slightly different angle.
  • Violet light is refracted through the largest angle.
  • Red light is refracted through the smallest angle.

Part 4 of 6Showing dispersion with a prism

1
Set up a ray box so that a ray of white light shines on a glass prism.
2
Place a white screen on the other side of the prism.
3
Adjust the positions of the prism and the screen until the colours of the spectrum appear.
4
Move the screen closer or further away to change the width of the spectrum.
  • Prism
    • a solid piece of glass or plastic with a triangular cross-section.

Part 5 of 6Rainbows

1Rainbow
  • Rainbow formed when drops of water in the air cause dispersion of light, which is also reflected inside the drops.
2Conditions for seeing a rainbow
  • Conditions for seeing a rainbow the Sun must be shining, there must be small drops of water in the air and the Sun must be behind the observer.

Part 6 of 6Safety

Safety
Keep the eye at least a metre from the prism because the light can be very bright.
Make the room as dark as possible.

Key terms

TermMeaning
White lightLight made of all the colours of the spectrum.
SpectrumThe range of colours in white light.
DispersionSplitting of white light into its colours.
PrismA transparent triangular block that disperses light.
RefractionThe change of direction of light when it passes between materials.

Avoid these mistakes

1
Rainbows are made only from rain — any water drops with sunlight can form one.
2
A prism adds the colours to the light — it splits the colours already in white light.
3
All colours are refracted by the same amount — violet is refracted most and red least.
4
A prism makes the light coloured by a filter — the colours are separated by refraction.

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