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Grades 6–8 Beginner About 15 min Version 1 Awaiting review Premium

Reflection of light: the angle game

Light travels in straight lines called rays. When a ray hits a mirror, it bounces off: it is reflected. Draw a line at right angles to the mirror where the ray hits it; this is the normal. The angle between the incoming ray and the normal is the angle of incidence (i), and the angle between the reflected ray and the normal is the angle of reflection (r). The law of reflection says i = r, and both rays and the normal lie in the same flat plane. A smooth mirror gives regular reflection; a rough surface scatters light in all directions (diffuse reflection).

What you will learn

  • Identify the incident ray, reflected ray and normal.
  • Show that the angle of reflection equals the angle of incidence.
  • Distinguish regular and diffuse reflection.

Before you start

  • Measure angles with a protractor.

Materials

  • Plane mirror, sheet of rough paper
  • White paper, pencil and protractor

Equipment

  • Ray box or torch with a slit

Procedure

  1. Shine the ray at the mirror at 20°, 40° and 60° to the normal, recording the angle of reflection each time.
  2. Shine the ray straight down the normal (0°) and record what happens.
  3. Replace the mirror with rough paper and record.

How this simulation is simplified

  • The mirror is perfectly flat and the ray is very thin.