Physics · KS3 and GCSE · Interactive lesson
Reflection and refraction of light
Follow a light ray at a mirror or a glass surface. Find the normal, measure angles and explore how reflection differs from refraction.
Choose your view
Explore an interactive example, then try the questions at your own pace.
KS3 / GCSE · start with the idea
By the end of this lesson: Measure reflection angles from the normal, not from the mirror.
The interactive diagram and controls are in Stage 2, “Explore one example”. Read the idea here, then try it next.
- The normal is an imaginary line at 90° to the mirror.
- Measure the incoming and reflected angles from the normal.
- The angle of reflection equals the angle of incidence.
Useful starting points
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What do the words mean?
- Normal
- An imaginary line at right angles (90°) to the surface where the ray arrives.
- Angle of incidence
- The angle between the incoming ray and the normal.
- Reflection
- Light returning into the material it came from at a surface.
- Refraction
- Light changing direction when it crosses into another material at an angle and changes speed.
Change the example
This is the lesson example. Your practice question uses its own numbers.
Something to try
Increase the angle of incidence. Compare it with the angle of reflection. Both are measured from the normal.
Notice what changes
How particle motion works +
Starts paused. Press Play, then add energy to see the warmer particles move faster.
Particles keep the same size. Liquid particles move around; solid particles vibrate around fixed positions. This is a simplified model, with the change in motion exaggerated to make it easier to see.
About the playback +
About this model
Follow the arrows. Orange shows light arriving at the flat mirror; purple shows it leaving. Measure both angles from the dashed normal. Ray lines show the path of the light, not its speed.
More about this diagram
Still picture. Play particle motion in Stage 2.
Reflection angle = 30°
Still picture of the example from Stage 2. Use the back arrow to change it.
Work through it
Starting example: read the steps below
- Find the surface where the materials meet. The dashed normal is at 90° to it.
- Measure the incoming angle from the normal: 30°.
- The reflected angle is also 30°.
- An angle to the surface would be 90° minus the angle to the normal.
Try on your own
Your turn. No rush.
Question 1
A ray hits a flat mirror. The normal is drawn at what angle to the mirror surface?
About these questions
Questions appear in a mixed order. Work at your own pace and stop whenever you like.
These questions use their own numbers, separate from the lesson example. You can stop whenever you like. Answers last for this visit to the page.
A good place to pause
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Can you find the normal and explain whether a ray is reflected or refracted?
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Notes for parents and tutors
These lessons cover selected KS3 and GCSE ideas for England; they are not a complete course. The level notes explain where GCSE methods or optional extensions begin. Maurice can help you choose material for your course and exam board.
The content draws on the DfE Maths curriculum, DfE Science curriculum and AQA GCSE Physics specification. Level labels are guidance, not exam-board endorsements. For AQA Radioactivity, calculating net decline as a ratio is Higher-tier work. Net means the overall change; ask Maurice whether this extension is relevant to your course. Explanations and practice were reviewed during development on 21 October 2026; Maurice should check their fit before assigning work.
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