AQA GCSE Physics

Revision Notes

6.3.6 Colour & Reflection of Light

Colour Filters

  • White light is a mixture of all the colours of the spectrum
  • Each colour has a different wavelength (and frequency), making up a very narrow part of the electromagnetic spectrum
  • White light may be separated into all its colours by passing it through a prism
    • This is done by refraction
    • Violet light is refracted the most, whilst red light is refracted the least
    • This splits up the colours to form a spectrum
  • This process is similar to how a rainbow is created

refraction-by-prism, IGCSE & GCSE Physics revision notes

White light may be separated into all its colours by passing it through a prism

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

Colour & Reflection of Light

  • The colour of an opaque object is determined by which wavelengths of light are more strongly reflected
  • Wavelengths that are not reflected are absorbed
    • Hence, this is why different objects appear to be different colours
  • For example, white light upon a green surface will only have green light reflected and the others absorbed
    • This light is reflected into our eyes to see the surface in that colour

green-surface, IGCSE & GCSE Physics revision notes

A green surface reflects green light and absorbs all other colours

  • An object will appear white if:
    • All wavelengths are reflected equally
  • An object will appear black if:
    • All wavelengths are absorbed
  • An object will appear transparent if:
    • All the light is transmitted, and only a small amount is reflected or absorbed

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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.
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