Reflection of Light (Cambridge (CIE) O Level Physics): Revision Note

Ray Diagrams

• Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary

  • The angle of the wave approaching the boundary is called the angle of incidence (i)

  • The angle of the wave leaving the boundary is called the angle of reflection (r)

• The line at right angles (90°) to the boundary is known as the normal

• When drawing a ray diagram an arrow is used to show the direction the wave is travelling

  • An incident ray has an arrow pointing towards the boundary

  • A reflected ray has an arrow pointing away from the boundary

• The angles of incidence and reflection are usually labelled i and r respectively

Reflection

A ray diagram for light reflecting at a boundary, showing the normal, angle of incidence and angle of reflection

The Law of Reflection

• The law of reflection states that these angles are the same:

Angle of incidence (i) = Angle of reflection (r)

Law of Reflection

Reflection of a wave at a boundary, i = r