Suggested practical

Investigation of reflection with a plane mirror

Aim of the experiment

A raybox shines an incident ray at an angle towards a plane mirror. This reflects the ray and reveals the angle of reflection and the normal, which is a central vertical line between the two angles.

To investigate the reflection of light by a plane mirror.


  1. Set up a ray box, slit and lens so that a narrow ray of light is produced.
  2. Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an 'N' for 'normal'.
  3. Place a plane mirror against the first line.
  4. Use the ray box to shine a ray of light at the point where the normal meets the mirror. This is the incident ray.
  5. The angle between the normal and the incident ray is called the angle of incidence. Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray reflected from the surface of the mirror.
  6. Using a pencil on the paper, mark the path of:
  7. Remove the mirror. Join the crosses to show the paths of the light rays.
  8. Measure the angle of incidence and angle of reflection for the mirror.
  9. Repeat steps 2 - 8 for several different angles of incidence.


Record results in a suitable table.

AttemptAngle of incidence (°)Angle of reflection (°)


Compare the angle of incidence with the angle of reflection for each block.


The light rays should obey the law of reflection for every attempt. To what extent do the results show this?


HazardConsequenceControl measures
Ray box gets hotMinor burns Do not touch bulb and allow time to cool
Semi-dark environmentIncreased trip hazardEnsure environment is clear of potential trip hazards before lowering lights