Reflection and Refraction of Waves
Understand Reflection and Refraction of Waves for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: waves can be reflected, refracted, transmitted or absorbed at a boundary, and refraction is caused by a change in wave speed.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
When a wave meets a boundary between two materials, it may be reflected, transmitted or absorbed. This is a Triple-only required practical.
Reflection occurs when the wave bounces off the boundary. The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal — a construction line drawn at right angles to the surface.
Refraction occurs when a wave is transmitted into a different material and changes direction. This happens because the wave changes speed. Entering a denser material the wave slows and bends towards the normal; leaving it the wave speeds up and bends away from the normal.
Revision notes
What happens at a boundary
A wave meeting a boundary may be reflected, transmitted or absorbed.
What happens depends on the wavelength of the wave and on the properties of the two materials.
Reflection
The angle of incidence equals the angle of reflection.
Both angles are measured from the normal, a construction line drawn at right angles to the surface at the point where the ray meets it. Measuring from the surface itself is a common error.
Refraction
Refraction is the change in direction of a wave entering a different material, caused by a change in wave speed.
Entering a denser material the wave slows and bends towards the normal. Leaving it the wave speeds up and bends away from the normal. A wave meeting the boundary along the normal does not change direction.
Key points
- Waves may be reflected, transmitted or absorbed.
- Angle of incidence equals angle of reflection.
- Angles are measured from the normal.
- The normal is at right angles to the surface.
- Refraction is caused by a change in wave speed.
- Entering a denser material bends the wave towards the normal.
Worked examples
Example 1
State the law of reflection. [2 marks]
Model answer
The angle of incidence is equal to the angle of reflection (1 mark), with both angles measured from the normal (1 mark).
Example 2
Explain why a light ray changes direction when it enters glass from air. [3 marks]
Model answer
The light slows down as it enters the denser glass (1 mark). This change in speed causes the ray to change direction (1 mark), bending towards the normal (1 mark).
Example 3
Explain why a wave travelling along the normal does not change direction when it enters a different material. [2 marks]
Model answer
The whole wavefront reaches the boundary at the same instant (1 mark), so although the wave changes speed, there is no change in direction (1 mark).
Common mistakes
Measuring angles from the surface.
All angles are measured from the normal, not the surface.
Saying refraction is caused by the material being denser.
It is caused by the change in wave SPEED at the boundary.
Getting the bending direction wrong.
Slowing down bends towards the normal; speeding up bends away.
Forgetting the normal-incidence case.
A wave along the normal changes speed but not direction.
Exam tips
- Always measure angles from the normal.
- Explain refraction through the change in wave speed.
- Learn the bending directions both ways.
- Remember this is a Triple-only required practical.
Key terms
- Normal
- A construction line at right angles to a surface.
- Angle of incidence
- The angle between the incoming ray and the normal.
- Reflection
- A wave bouncing off a boundary.
- Refraction
- A change in direction caused by a change in wave speed.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.