O-Level Physics Law of Reflection Practical: Rays, Angles and Safety
Investigate reflection with a ray box and plane mirror.
- Measure angles from the normal, compare readings and understand the precautions at each step.
The law of reflection compares two angles: the angle between the incoming ray and the normal, and the angle between the reflected ray and the same normal. Measuring from the mirror surface instead gives the wrong quantities.
This guide uses a supervised ray-box investigation as its example. Follow the apparatus instructions and your teacher's briefing before starting. General preparation and supervision are explained in Lab safety starts before the experiment.
What you are investigating
Draw a normal perpendicular to a plane mirror at the point where the light strikes. Measure the angle of incidence and the angle of reflection for several incoming directions. The relationship to test is that the two angles are equal.
The 2026 SEAB Physics syllabus, 6091, lists investigating the law of reflection among its practical exercises on page 31. Its light topic defines the angles on page 20. This is distinct from finding the position of an image in a plane mirror; one investigation does not replace the other.
Set up a single visible ray
Use white paper, a pencil, ruler, protractor, a plane mirror in a holder and a ray box with a single slit. Use only the power supply specified for that apparatus. The Institute of Physics reference activity
Sources
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