Required practical - Investigating refraction (AQA GCSE Physics): Revision Notes
Required practical - Investigating refraction
This is a key practical you need to know for your GCSE physics exam. You'll investigate how light changes direction when it moves between different materials.
This practical is frequently tested in GCSE physics exams. Understanding both the method and the underlying physics concepts is essential for exam success.
What is the aim?
The aim is to investigate how light waves change direction when they move from air into other transparent materials like glass or Perspex.
Equipment you need
Required Equipment List
Make sure you have all these items before starting the experiment:
- Ray box with lens and slits
- 12V power supply
- Glass block (rectangular)
- Perspex block (rectangular)
- Ruler
- Protractor
- A3 paper
- Sharp pencil
Method - step by step
Worked Method: Step-by-Step Refraction Investigation
Follow these steps carefully to get accurate results:
Step 1: Place the rectangular block on A3 paper. Draw around it with a sharp pencil.
Step 2: Draw the normal line. This goes at right angles to the side of the block where the light ray will enter.
Step 3: Use your protractor and pencil to mark angles on the paper. Mark every 10° from 0° up to 80°.
Step 4: Start with 0° (light travelling along the normal line). Direct the light ray towards the block and mark where it exits with a sharp pencil dot.
Step 5: Remove the glass block. Join the entry point to the exit point with a straight line. Measure this angle - this is the angle of refraction.
Step 6: Repeat for all angles from 10° to 80°.
Step 7: Repeat the whole experiment using the Perspex block.
Important safety notes
Safety Precautions - Read Before Starting
- The ray box gets hot when used for long periods
- Be careful not to burn your skin
- Handle glass blocks carefully to avoid breakage
Typical results
Your results should look similar to this:
| Angle of incidence | Angle of refraction (Glass) | Angle of refraction (Perspex) |
|---|---|---|
| 0° | 0° | 0° |
| 10° | 7° | 7° |
| 20° | 13° | 13° |
| 30° | 19° | 20° |
| 40° | 25° | 27° |
| 50° | 31° | 33° |
| 60° | 35° | 40° |
Notice how the angle of refraction is always smaller than the angle of incidence, and glass bends light more than Perspex at higher angles.
What happens and why?
Refraction is when light changes direction as it moves from one material to another. Two things change:
- Direction of the light ray (unless travelling along the normal)
- Speed of the light
Light slows down when moving from air into glass. Light speeds up when moving from glass back into air.
Key points about refraction
Understanding refraction involves several important concepts that explain the behaviour of light as it moves between different materials.
Key Refraction Concepts
- The angle of refraction is always smaller than the angle of incidence when light enters a denser material
- Glass is more optically dense than Perspex, so it bends light more
- When light travels along the normal line (0°), there is no change in direction
- All angles are measured from the normal line, not from the surface
Conclusion
When light travels from air into a glass block, its direction and speed both change. The angle of refraction is smaller than the angle of incidence unless the light is travelling along the normal. Glass causes more refraction than Perspex because glass is more optically dense and slows the light down more.
Key Points to Remember:
- Refraction happens when light changes speed moving between materials
- Light slows down entering glass, speeds up leaving glass
- The normal line is perpendicular to the surface - measure all angles from here
- Glass bends light more than Perspex because it's more optically dense
- No bending occurs when light travels along the normal (0° angle)