Wave properties

Before we dive into the wave-particle duality of light, we first need to refresh our memories and remind ourselves the main properties of waves. The diagram below labels some of the important features of a wave.

Reflection & Refraction

When light hits a surface, it can reflect off that surface. When it does reflect, the angle of incidence the wave makes to the normal equals to the angle of reflection, as seen in the diagram below.

When light enter a different medium (for example, from water to air), its speed changes and hence its direction changes too. Below are two common examples of how the direction of light changes as it travels from air to glass and glass to air.

*diagram*

Diffraction

Diffraction is the name given to the effect when a straight wave passes through a narrow opening; the wave bends around the opening as seen in the diagram below.

*diagram*

The effect of diffraction is greatest when the width of the opening is equal to or smaller than the wavelength of the wave.

Polarisation

Polarisation is the phenomenon where a transverse wave is only allowed to vibrate in one direction. Usually waves, for example light, vibrates in all directions. Once light has gone through a vertical polariser, it will only vibrate in the vertical direction.

Imagine a wave a travelling at 45 degrees to the horizontal. Once it goes through a vertical polariser, only the vertical component of the incoming wave will get through, and the outcoming wave will only vibrate in the vertical direction. This outcoming wave will have a smaller amplitude than the original wave.

Note that polarisers can be at any direction; vertical, horizontal, or at any degree.