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Year 8

The visible spectrum

I can describe what white light is, and explain why a visible spectrum can be produced from white light.

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New
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Year 8

The visible spectrum

I can describe what white light is, and explain why a visible spectrum can be produced from white light.

Download all resources
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Share activities with pupils
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Lesson details

Key learning points

  1. White light from the Sun and light bulbs consists of light of all the colours in the visible light spectrum (a rainbow).
  2. A transparent triangular prism can split up sunlight into a visible light spectrum.
  3. The visible light spectrum shows the range of colours that light can have.
  4. Cone cells in the eye detect colour. There are 3 kinds (R, G and B); each is sensitive to a range of colours of light.
  5. The colour we see depends on which cone cells are triggered to send a signal to the brain.

Keywords

  • White light - Light that consists of red, green and blue light in equal amounts so looks white.

  • Triangular prism - A uniform 3D shape with triangular ends.

  • Visible light spectrum - A rainbow pattern of coloured light that always occurs with the colours in the same order.

  • Cone cells - The cells at the back of the eye that detect colour.

Common misconception

Sunlight is yellow(ish), not white.

Show pupils a yellow light (and illuminate white paper beneath a yellow light) and compare it to sunlight to show that sunlight is white.

Our eyes detect all colours of light (not just R, G and B). Each kind of cone cell detects a different range of wavelengths, and the three ranges overlap (e.g. yellow light of a single wavelength triggers both the 'R' and 'G' cones). The concept of wavelength of light is best left until later units.
Teacher tip

Equipment

Ray lamps, slits, transparent triangular prisms, red filters (to fit in the ray lamps).

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
A person has an object that they can see through clearly. The object transmits light so it can be described as being...
Correct answer: transparent.
translucent.
opaque.
invisible.
Q2.
The back surface of the eye that detects light is called the .
Correct Answer: retina
Q3.
How many types of cone cell are in the eye of a person who has full colour vision?
0
1
2
Correct answer: 3
Q4.
Which of the following explains why we see mainly in shades of grey in dim light?
The pupil becomes larger in dim light.
The rod cells do not work well in dim light.
Correct answer: The cone cells do not work well in dim light.
The cone cells all become equally sensitive in dim light.
Q5.
Match each set of colours of light with the colour that is seen when they enter a person's eyes. (All of the colours in each set have equal brightness.)
Correct Answer:blue and green light,cyan

cyan

Correct Answer:blue and red light,magenta

magenta

Correct Answer:green and red light,yellow

yellow

Correct Answer:blue, red and green light,white

white

Correct Answer:no light,black

black

Q6.
The screen on a mobile phone shows a yellow banana. Which of the following explains how it does this?
The screen contains yellow coloured dye.
The screen has tiny yellow lights, and these lights are switched on.
Correct answer: The screen displays two colours of light and neither of these is yellow.
The screen splits white light into a rainbow of colours and shows the yellow.

Exit quiz

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6 Questions

Q1.
A rainbow shows the colours that white light can be separated into. They are always in the same order. This is called the visible light...
band.
plectrum.
range.
scale.
Correct answer: spectrum.
Q2.
The diagram shows a 3D shape called a __________. When this shape is made out of glass or clear plastic, it can split white light into its component colours.
An image in a quiz
polygon
pyramid
triangle
tetrahedron
Correct answer: triangular prism
Q3.
Although a rainbow is actually a continuous range of colours, it is traditionally described as having seven colours. Starting with red, sort the seven colours of a rainbow into the correct order.
1 - red
2 - orange
3 - yellow
4 - green
5 - blue
6 - indigo
7 - violet
Q4.
Which of the following statements describes how a rainbow is made?
Each raindrop makes all of the colours of light.
Different raindrops make different colours of light.
Correct answer: Raindrops split white light into all of its colours.
Raindrops absorb some colours of white light but not the colours of the rainbow.
Q5.
Which of the following can look like white light when it enters our eyes at the same time?
a combination of equal brightness of red and green light
Correct answer: a combination of equal brightness of red, green and blue light
a combination of equal brightness of red, yellow and blue light
Correct answer: a combination of equal brightness of all of the colours of visible light
Q6.
A person looks at a television screen and sees cyan, a secondary colour of light. Which of the following statements are correct?
The colour cyan does not appear in a rainbow.
Light from the screen is detected by the R cone cells of the person’s eyes.
Correct answer: Light from the screen is detected by the G cone cells of the person’s eyes.
Correct answer: Light from the screen is detected by the B cone cells of the person’s eyes.
Correct answer: The signal to their brain is the same as when they see a cyan object.

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