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3.3Unit 6: Light and objects in space

Making rainbows — Cambridge Checkpoint Physics 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 4 of 8 1 quiz

📚 Cambridge Checkpoint Physics 0893 Hub / Topical Revision
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Lesson summary

3.3 Making rainbows — CHECKPOINT PHYSICS 0893 notes: Explain dispersion of white light into the spectrum, the order of the colours and how rainbows form.Experiment — in 1666 Newton used a triangular glass prism to split sunlight from a small hole onto a screenResult — white light…

  • Memory aid
  • Number of colours
  • Least bent
  • Water drops
  • Other sources
  • Seven colours

Section 1 of 8Newton's discovery

Experiment
  • Experiment in 1666 Newton used a triangular glass prism to split sunlight from a small hole onto a screen
Result
  • Result white light is made of many colours
Prism
Prism a solid transparent shape, such as a triangular glass block

Section 2 of 8The spectrum

Spectrum
Spectrum the range of colours seen in white light
Merging
  • Merging the colours merge from one to another
Order
  • Order red, orange, yellow, green, blue, indigo, violet
Memory aid
  • Memory aid the name ROY G.
  • BIV
Number of colours
  • Number of colours most people agree on seven, although some people see five or six, with indigo and violet looking the same

Section 3 of 8Dispersion

Dispersion
Dispersion splitting white light into different colours
Cause
  • Cause each colour is refracted through a slightly different angle
Least bent
  • Least bent red light is refracted through the smallest angle
Most bent
  • Most bent violet light is refracted through the largest angle

Section 4 of 8Rainbows

Formation
  • Formation water drops in the air cause dispersion of sunlight and reflect the light inside the drop
Sun
  • Sun it must be shining to give bright light
Water drops
  • Water drops there must be rain or small drops in the air
Position
  • Position the Sun must be behind the observer because the drops reflect the light back
Other sources
  • Other sources a hosepipe spray on a sunny day can make a rainbow

Section 5 of 8Making a rainbow with a prism

1
Darken the room and set up a ray box so a ray of light passes through a prism onto a screen.
2
Adjust the positions until a spectrum appears on the screen.
3
Move the screen closer to the prism, and then further away, and observe the colours.
4
Remove the screen and look into the refracted rays from about 1 metre and then 2 metres away.
5
Move from side to side to see the different colours.

Section 6 of 8Observations in the prism investigation

Seven colours
  • Seven colours they appear in order from red to violet
Screen closer
  • Screen closer the colours are closer together and less spread out
Screen further
  • Screen further the colours are more spread out
Safety
  • Safety keep the eye at a safe distance from the prism, because the light can become very bright
Analogy
  • Analogy the prism is a model of water drops forming a rainbow

Section 7 of 8Key terms

TermMeaning
DispersionSplitting of white light into its colours.
SpectrumRange of colours in white light.
PrismTriangular block of glass that disperses light.
RefractionChange of direction of light due to speed change.
RainbowSpectrum formed by water drops in sunlight.

Section 8 of 8Exam technique

1
Thinking a rainbow needs the Sun in front — the Sun is behind the observer.
2
Thinking the prism adds colour — it only separates colours already in white light.
3
Thinking red is bent most — violet is refracted through the largest angle.
4
Mixing up dispersion and reflection — dispersion is the splitting of white light into colours.

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