Wave & particle models of light

There are six main properties of light that should be explained by a theory of light. The wave model and the particle model explain them with varying degrees of success.

linear propagation

Light propagates in straight lines. It does not fall and hit the floor.

  • Particle: light is composed of very small, fast-moving particles.
  • Wave: no good explanation.

Light diffracts when it passes through a slit.

  • Particle: particles collide with the sides of the slit and scatter.
  • Wave: water analogy.

Light reflects off many surfaces.

  • Particle: pool table analogy.
  • Wave: water analogy.

Light refracts when it enters a different medium.

  • Particle: the particles move at different speeds in different media.
  • Wave: water analogy.
partial reflection & refraction

Window panes reflect part of the incoming light and transmit the rest, depending on the viewing angle.

  • Particle: no good explanation.
  • Wave: water analogy.
dispersion of white light

White light disperses into the colours of the rainbow when it passes through a prism.

  • Particle: different colours of light are made of particles of slightly different mass (red is heavy, violet is less heavy).
  • Wave: each colour is a wave with a different wavelength (red is long, violet is short).

The wave model seems to do a better job of explaining most of these properties, but in reality the answer is more complicated than that.