The Laws of Reflection - October 25, 2024

The Incident and Reflected Ray

  • The TWO laws of reflection:

  1. The angle of incidence = the angle of reflection

  2. The incident ray, the reflected ray, and the normal all lie in the plane

How to Illustrate The Law of Reflection

  1. Draw the incident ray using a ruler

  2. At the contact point where the incident ray hits the surface, draw a normal by measuring a 90 degree angle with a protractor

  3. Measure the angle of incidence (i) between the incident ray and the normal. Make a mark to indicate the same angle on the other side of the normal. This is the angle of reflection (r)

  4. Draw the reflected ray from the contact point through the mark using a ruler

  5. Label the incident ray, the reflected ray, the angle of incidence (i), the angle of reflection (r) and the normal

Reflecting Light Off Surfaces - Regular Reflection

  • The reflection of light off a smooth, shiny surface (e.g. plane mirror, very still water, flat aluminum foil) → called a specular reflection

  • If the parallel incident rays strike a flat surface, angles of incidence are all identical

  • Therefore, angles of reflection will all be identical, and reflected rays are all parallel to each other

  • Disco mirror ball has many plane mirrors on a spherical surface that reflect light in all directions.

Diffuse Reflection

  • The reflection of light off an irregular or dull surface (e.g. sheet of paper, water surface with waves, crumpled aluminum foil)

  • Diffuse reflection can also be referred to as the scattering of light which makes non-luminous objects visible

Reflecting Light Off Surfaces

  • Incident rays would all have different angles of incidence, therefore different angles of reflection and reflected rays would reflect/scatter in many different directions!

Reflection and Dyslexia

  • People who suffer from dyslexia complain about the glare off white → there is too much reflected light from the paper

  • The contrast between the white paper and black text makes it very difficult for them to read print

  • Correction: coloured filters or glasses are used that reduce the glare of reflected light off the paper