Light & Surfaces (Edexcel GCSE Physics)

Specular Reflection

• Specular reflection is defined as:

Reflection from a smooth surface in a single direction

• When light reflects off a smooth surface, such as a mirror, specular reflection occurs
  • This is what gives a mirror its shiny appearance

• This is why a reflection can be seen clearly in a mirror
• In this case, the angle of reflection r is equal to the angle of incidence i

When reflecting off a mirror, the specular reflection occurs. The angle of incidence is equal to the angle of reflection

Diffuse Reflection

• Diffuse reflection is defined as:

Reflection from a rough surface causes scattering

• When light reflects off a rough surface, which applies to the majority of surfaces, diffuse reflection occurs
  • This is what gives objects a dull or matt appearance

• This is why a reflection cannot be seen clearly from a table surface, for example
  • Even though a table's surface may look smooth from afar, it is actually made up of many tiny ridges which the light rays are scattered off

• When light scatters, it leaves the surface in all directions

When light is reflected from the majority of surfaces it is scattered – a process known as diffuse reflection

Differential Absorption of Colour

The object is seen as red since the red light is reflected whilst the other colours are absorbed

Colour Filters

• Colour filters work by absorbing certain wavelengths and transmitting other wavelengths
  • These certain wavelengths correspond to certain colours

• When white light passes through a coloured filter, some colours are absorbed whilst others are able to pass straight through
• For example, when white light passes through a red filter:
  • Red light is transmitted
  • All the other colours are absorbed

• The colour that is transmitted is the same colour as the filter

A red filter transmits only red light and absorbs all other colours of light