A student is investigating waves at a boundary between two different materials. The student notices that when a wave travelling through one material reaches the boundary with a second material, some of the wave passes into the second material and some of the wave bounces back. Explain what happens to a wave at a boundary between two materials, referring to both transmission and reflection.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Waves can behave in different ways when they reach a boundary between two different materials. The behaviour depends on the properties of the two materials.
Model answer (4 marks)
When a wave reaches a boundary between two media, part of its energy is transmitted into the second medium and part is reflected back into the first.
The transmitted part continues into the second material, often changing direction – this is refraction – because the wave speed differs in the two media.
The reflected part travels back into the first medium. For the reflected wave the angle of reflection equals the angle of incidence.
Thus at a boundary waves are partially transmitted (and refracted) and partially reflected, with the reflected angle equal to the incident angle.
The transmitted part continues into the second material, often changing direction – this is refraction – because the wave speed differs in the two media.
The reflected part travels back into the first medium. For the reflected wave the angle of reflection equals the angle of incidence.
Thus at a boundary waves are partially transmitted (and refracted) and partially reflected, with the reflected angle equal to the incident angle.
Examiner tips
- Use the words ‘transmitted’ and ‘reflected’ explicitly; mention refraction for the transmitted wave.
- State the equality of angles for the reflected wave – examiners look for this detail.
- Keep the answer concise – 4 marks allow a short paragraph, not a long explanation.
Common mistakes
- Saying the wave is either transmitted or reflected but not both.
- Forgetting to mention that the transmitted wave can change direction (refraction).
- Confusing the angle of incidence with the angle of transmission – the equality applies only to the reflected wave.
Mark scheme (4 marks)
- Some of the wave is transmitted through the boundary into the second material
- The transmitted wave may change direction / be refracted at the boundary
- Some of the wave is reflected back at the boundary
- The angle of reflection equals the angle of incidence (for the reflected wave)
Key terms in this question
transmission · reflection · boundary
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Wave behaviour questions
- Explain what happens to a wave when it passes from deep water into shallow water…
- Describe what happens to a light wave when it travels from air into glass, in te…
- A harbour wall has a narrow opening that allows ocean waves to enter a sheltered…
- A teacher demonstrates sound waves passing through a narrow gap in a wall. The t…