Science at key stage 3 (Year 8)
Unit 8K: Light
Section 1: a. How does light travel?
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Objectives |
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- that light travels from a source
- that light travels at a very high speed, much faster than sound
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Activities |
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Outcomes |
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Children: |
- Review pupils' understanding of light by asking them
Where is there light in this room? Help them to develop the idea of light travelling and to recognise that although, when a light is switched on, its effects on objects seem instantaneous, this is because light travels at immense speed. Recall their experience of thunder and lightning, to show that light travels much faster than sound.
- Ask pupils for suggestions on how we could show that light moves,
eg how a lighthouse works. Help pupils to carry out a thought experiment. Ask them to imagine what would happen if the source were moved further and further away from an object, and help them to understand that, at great distances, there is a lapse of time between leaving one and meeting the other. Some will have heard of the speed of light. Help them towards an understanding of this very large number by relating it to everyday speeds and distances, and comparing these with the distance between stars.
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- recognise that light is all around
- state that light travels much faster than sound
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Points to note |
- Some pupils respond to the question
Where is there light in this room? by identifying light sources rather than the idea that light is all around. Recognition that light radiates from a source implies that it is moving. Some pupils may believe that this movement of light applies only to very strong sources,
eg the Sun, and that light from a weak source,
eg a torch bulb, is different and slower.
- The speed of light is 300,000 km/s, and it thus takes light from the Sun 8.5 minutes to reach Earth, and reflected light from the Moon 1.3 seconds. Light from the nearest star (other than the Sun) takes 4 years to reach us.
- In unit 7L 'The solar system and beyond' pupils will have considered the solar system and stars. They will not have considered distances in terms of light.
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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