Course: Separate Physics only | Tier: Foundation + Higher
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Aim
To investigate the reflection of light by different surfaces and the refraction of light by different substances.
Method
- Place a glass (or Perspex) block on paper and draw around it. Draw a normal at 90° to one side.
- In a darkened room, shine a narrow ray of light from a ray box at the point where the normal meets the block.
- Mark the paths of the incident, reflected and refracted rays with small crosses, then join them up with a ruler.
- Measure the angles of incidence, reflection and refraction from the normal with a protractor.
- Repeat for different angles of incidence and for different materials.
| Independent variable | Angle of incidence (or material of block) |
| Dependent variable | Angle of refraction (or angle of reflection) |
| Control variables | Width of the ray; the same ray box; same block when varying angle |
Questions
Q1 (F) Name the independent and dependent variables when investigating refraction.
Show answer
Independent: angle of incidence. Dependent: angle of refraction.
Q2 (F) What is the normal?
Show answer
A line drawn at 90° to the surface at the point where the ray hits it. All angles are measured from the normal.
Q3 (F) How can you mark the path of a ray accurately?
Show answer
Use a narrow ray in a darkened room. Mark the centre of the ray with small crosses spaced well apart, then join them with a ruler and a sharp pencil.
Q4 (F) What result would you expect for reflection from a plane mirror?
Show answer
The angle of incidence equals the angle of reflection.
Q5 (F/H) A ray enters a glass block at an angle of incidence of 40°. The angle of refraction is 25°. Explain what happens to the ray.
Show answer
The ray bends towards the normal, because light slows down when it enters glass from air.
Q6 (F/H) Why does a ray that enters along the normal not change direction?
Show answer
The angle of incidence is 0°. The light still slows down, but because the whole wavefront enters the glass at the same time, it does not change direction.
Q7 (F/H) State one hazard and how to reduce the risk.
Show answer
The ray box gets hot – don’t touch the bulb and let it cool before packing away. The room is dark – keep bags and stools out of the walkways.
Q8 (H) The ray drawn on the paper is quite wide. Explain how this affects the results and how to improve them.
Show answer
A wide ray makes it hard to judge exactly where its centre is, so the measured angles are less accurate. Use a narrower slit in the ray box, mark the centre of the ray, and repeat each angle to calculate a mean.
