AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
(HT only) Some effects, for example refraction, are due to the difference…
Full specification wording
Properties of electromagnetic waves 1: (HT only) Some effects, for example refraction, are due to the difference in velocity of the waves in different substances.
Refraction happens because a wave changes speed when it crosses a boundary between substances.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 2 of 5
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Refraction happens because a wave changes speed when it crosses a boundary between substances. If the wave slows down, it bends towards the normal; if it speeds up, it bends away from the normal. The velocity depends on the substance, so the same wave can travel at different speeds in different materials. For example, light travels more slowly in glass than in air, so a ray entering glass at an angle bends towards the normal, and leaving glass it speeds up and bends away. When explaining refraction, identify the boundary, state which substance the wave speeds up or slows down in, and link that change to the direction of bending.
What earns the marks
- Refraction is caused by a change in the velocity of the wave when it passes from one substance to another.
- If the wave slows down at a boundary, it bends towards the normal.
- If the wave speeds up at a boundary, it bends away from the normal.
- The velocity of an electromagnetic wave depends on the substance it is travelling through, so different substances give different speeds.
Common mistakes and how to put them right
Saying refraction is caused by the wave 'hitting' the surface or by reflection.
Put it right: Refraction is caused by a change in velocity as the wave enters a different substance.
Mixing up the direction of bending.
Put it right: Slower in the new substance means bending towards the normal; faster means bending away from the normal.
Thinking the velocity of light is the same in all substances.
Put it right: The velocity depends on the substance, which is why refraction occurs.
Exam tips
- Always name the two substances and state whether the wave speeds up or slows down before describing the bending.
- Link the change in velocity to the change in direction in one clear causal sentence, for example 'because it slows down in glass, it bends towards the normal'.
Try the lesson
The start of the Properties of electromagnetic waves 1: (HT only) Some effects, for example refraction, are due to the difference in velocity of the waves in different substances. lesson, made from checked teaching notes for this specification point.
Have a go first
A light ray passes from air into a glass block. Why does the ray change direction at the boundary between the air and the glass?
Listen
Refraction happens because a wave changes speed when it crosses a boundary between substances. If the wave slows down, it bends towards the normal; if it speeds up, it bends away from the normal. The velocity depends on the substance, so the same wave can travel at different speeds in different materials. For example, light travels more slowly in glass than in air, so a ray entering glass at an angle bends towards the normal, and leaving glass it speeds up and bends away. When explaining refraction, identify the boundary, state which substance the wave speeds up or slows down in, and link that change to the direction of bending. A strong answer earns marks for these points. Refraction is caused by a change in the velocity of the wave when it passes from one substance to another. If the wave slows down at a boundary, it bends towards the normal. If the wave speeds up at a boundary, it bends away from the normal. The velocity of an electromagnetic wave depends on the substance it is travelling through, so different substances give different speeds. A common slip: Saying refraction is caused by the wave 'hitting' the surface or by reflection. Instead, refraction is caused by a change in velocity as the wave enters a different substance. Exam tip: Always name the two substances and state whether the wave speeds up or slows down before describing the bending.
See it
Key words
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Refraction
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Velocity of waves in different substances
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Direction of bending relative to the normal
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See every definition
- Refraction
- An effect that is due to the difference in velocity of the waves in different substances.
- Velocity of waves in different substances
- The velocity depends on the substance, so the same wave can travel at different speeds in different materials.
- Direction of bending relative to the normal
- If the wave slows down, it bends towards the normal; if it speeds up, it bends away from the normal.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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