AQA GCSE Physics · WavesTriple only
Reflection and refraction required practical
Investigate the reflection of light by different surfaces and the refraction of light by different substances.
You shine a thin ray of light into a glass block and trace where it goes. Measuring the angles from the normal shows that light bends towards the normal as it slows down entering glass.
This one is only on the separate Physics GCSE, so it won’t come up in Combined Science.
Equipment
- Ray box with a slit, and a power supply
- Rectangular glass block (and a perspex block, plane mirror)
- Protractor and ruler
- Sharp pencil and plain paper
Variables
- Independent you change
- Angle of incidence
- Dependent you measure
- Angle of refraction (or reflection)
- Control you keep the same
- Same block material
- Same ray box and slit width
- Measure all angles from the normal
Method
- 1
Put the glass block on paper and draw around it. Draw a normal (at 90° to the surface) where the ray will enter.
- 2
Shine a thin ray at the block so it hits the surface where the normal meets it.
- 3
Mark the ray going in and coming out with small crosses, then remove the block.
- 4
Join the crosses to draw the ray, including its path through the block.
- 5
Measure the angle of incidence and the angle of refraction from the normal with a protractor.
- 6
Repeat for different angles of incidence, and for a perspex block. For reflection, use a mirror and compare angles of incidence and reflection.
Worked example
Ray entering a glass block, angles measured from the normal.
| Angle of incidence (°) | Angle of refraction (°) |
|---|---|
| 0 | 0 |
| 20 | 13 |
| 30 | 19 |
| 40 | 25 |
| 50 | 31 |
| 60 | 35 |
Conclusion
The angle of refraction is always smaller than the angle of incidence: light bends towards the normal as it enters glass, because it slows down. At 0° it goes straight through. For a mirror, the angle of reflection always equals the angle of incidence.
Risks
- Ray box gets hotDon’t touch the bulb; switch it off when not in use.
- Working in a darkened roomKeep bags and stools out of walkways.
- Glass block edges can chip or cutHandle it carefully and report chips.
Common mistakes
- Measuring angles from the surface instead of from the normal.
- Using a wide beam. A thin ray is needed to mark its path accurately.
- Saying light bends away from the normal entering glass. It bends towards the normal as it slows down.
Better results
- Use a narrow slit so the ray is thin and easy to mark.
- Mark the ray with crosses far apart to draw its direction more accurately.
- Repeat each angle and calculate a mean angle of refraction.
Launching November 2026
7 exam questions on this practical.
Practise the method, the variables, the maths and what the results mean, then revise the Waves flashcards. It opens to students soon: join the waitlist and we’ll email you once, when it does.