Light & Surfaces (Edexcel GCSE Physics)

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Katie M

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Specular & Diffuse Reflection

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

Light Reflection, downloadable IGCSE & GCSE Physics revision notes

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

diffuse-reflection, IGCSE & GCSE Physics revision notes

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

Colour

Differential Absorption of Colour

  • Absorption occurs when:

Energy is transferred from the wave into the particles of a substance

  • Waves can be partially or completely absorbed
    • Sound waves are absorbed by brick or concrete in houses

  • Light will be absorbed if the frequency of light matches the energy levels of the electrons
    • The light will be absorbed, and then reemitted over time as heat

  • If an object appears red, this means:
    • Only red light has been reflected
    • All the other frequencies of visible light have been absorbed

Absorption, downloadable IGCSE & GCSE Physics revision notes

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

red-filter, IGCSE & GCSE Physics revision notes

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

Examiner Tip

Remember that the smaller the wavelength, the greater the refraction

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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.