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Visible Light Spectrum

  • Each colour within the visible light spectrum corresponds to a narrow band of wavelength and frequency
  • The different colours of waves correspond to different wavelengths:
  • Red has the longest wavelength (and the lowest frequency and energy)
  • Violet has the shortest wavelength (and the highest frequency and energy)

Colours of the visible spectrum with increasing wavelengthColours of the visible spectrum with increasing wavelength

  • Wavelength and frequency are inversely proportional, this means that:
    • An increase in wavelength is a decrease in frequency (towards the red end of the spectrum)
    • A decrease in wavelength is an increase in frequency (towards the violet end of the spectrum)

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 is equal to the angle of incidence i

Visible Light Spectrum & Reflection of Light | Physics for Grade 10When 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 reflectionWhen light is reflected from the majority of surfaces it is scattered – a process known as diffuse reflection

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

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

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

A green surface reflects green light and absorbs all other coloursA 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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