Explain what changes at a boundary
Reflection sends a wave back. Refraction occurs when speed changes in a new medium. Diffraction is strongest when the gap size is similar to the wavelength and spreading increases around narrower gaps.
GCSE Physics resources
AQA GCSE Waves
Reflection, Refraction and Diffraction
Reflection sends a wave back. Refraction occurs when speed changes in a new medium. Diffraction is strongest when the gap size is similar to the wavelength and spreading increases around narrower gaps.
Start here
The quick revision snapshot
Reflection sends a wave back. Refraction occurs when speed changes in a new medium. Diffraction is strongest when the gap size is similar to the wavelength and spreading increases around narrower gaps.
By the end, you should be able to…
- Explain explain what changes at a boundary using precise physics language.
- Apply the relevant equations, diagrams or practical method to an exam-style situation.
- Use the mini quizzes and practice answers to identify and correct a misconception.
Core learning content
Learn the idea before you practise it
Start with this short teaching sequence for Reflection, Refraction and Diffraction. Read the model, use the visual, then test your recall before moving into examples and exam practice.
Build the picture
At a reflecting boundary, the wave returns to the original medium. Refraction happens because speed changes at a boundary, changing wavelength and often direction. Diffraction is spreading after a gap or edge and becomes most obvious when the gap is similar in size to the wavelength.
Use the right relationship
Choose a relationship because of the physical change in the question, not because it is familiar. Wave speed: v = fλ (m/s, Hz, m). Period: T = 1 ÷ f (s, Hz). Magnification: magnification = image height ÷ object height (no unit). Keep the unit next to each value while you substitute.
What a strong answer does
Draw the normal where needed, label angles from the normal and explain the path using speed, wavelength and boundary conditions. Before writing, underline the command word and identify the information that matters. Keep a calculation as equation, substitution and answer with unit; keep an explanation as a linked chain using because, so or therefore. Finish by checking that the final sentence answers the exact context in the question and that the number, direction or conclusion agrees with the evidence given.
Retrieval practice
Quick checks
Answer without looking back first. The feedback explains the model, so a wrong answer still helps you learn.
Mini quiz 1
Check the core idea
Mini quiz 2
Apply the model
Mini quiz 3
Use exam precision
Try it
Wave boundary explorer
What changes when a wave meets a boundary or gap?
What to notice: the readout and written explanation remain available if you do not use the controls.
Worked examples
See the method being built
Cover the answer, attempt the method and then compare your physics language as well as the number.
Example 1 · Reflection law
A ray meets a mirror at 35° to the normal. Find reflection angle.
- Angles are measured from normal.
- Use angle i = angle r.
- Give degrees.
Show the answer
Reflection angle = 35°.
Example 2 · Refraction
A light ray enters glass from air and bends towards the normal. Explain.
- Identify new medium.
- State speed decreases.
- Link to change in direction.
Show the answer
Light slows in glass, so it refracts towards the normal.
Example 3 · Diffraction
Compare a 1 cm gap and 10 cm gap for 2 cm waves.
- Compare gap with wavelength.
- Identify stronger spreading.
- State conclusion.
Show the answer
Diffraction is strongest at the 1 cm gap because its size is similar to the 2 cm wavelength.
Misconception clinic
Common wrong turns
Each of these is tempting because it sounds almost right. Replace it with the precise physics before you meet it in a question.
- Measuring from the surface.
- Calling any bend reflection.
- Saying diffraction only happens at a gap.
Independent practice
Exam-style questions
Use the working space first. Reveal the guidance only after you have committed to an answer, then improve the exact part that would gain the next mark.
1. State the law of reflection.
[1 mark]Show answer and marking guidance
Angle of incidence equals angle of reflection.
2. State what happens to wave speed during refraction.
[1 mark]Show answer and marking guidance
It changes on entering a different medium.
3. State when diffraction is most noticeable.
[1 mark]Show answer and marking guidance
When gap size is similar to wavelength.
4. Why draw a normal?
[2 marks]Show answer and marking guidance
Angles of incidence, reflection and refraction are measured from it.
5. A ray hits a mirror at 50° to the normal. Find reflected angle.
[2 marks]Show answer and marking guidance
50°.
6. Explain why a wave does not change frequency on refraction.
[3 marks]Show answer and marking guidance
The source still produces the same number of waves per second; speed and wavelength change instead.
Questions pupils ask
GCSE Physics FAQs
What is the key idea in Reflection, Refraction and Diffraction?
A wave transfers energy without transferring matter overall. Use diagrams to keep amplitude, wavelength, frequency, speed and direction distinct.
How should I practise Reflection, Refraction and Diffraction?
Read the snapshot, attempt the worked examples without looking, complete the mini quizzes and then use the practice questions to check your wording and method.
Next step
Keep your revision moving
Physics sticks when you move between explanation, retrieval and application.