Dispersion and chromatic aberration

This page supports the multimedia tutorial Geometrical Optics.

Refraction depends on wavelength
Refraction from glass to air

In this experiment, a beam of white light is incident on the glass-air interface at an angle close to the critical angle. The different wavelenths are refracted with different angles, blue further than red. From Snell's law (and because the refactive of air is close to oen), this shows that the refractive index of glass is greater for glass than for air.

Therefore focal length depends on wavelength
Focal length is different for red and blue light

This experiment uses two-dimensional lenses: their surfaces are cylindrical, rather than spherical. Here, we show successively (i) three parallel rays of white light, (ii) the same with a red filter and (iii) the same with a blue filter. This shows the different focal length for red light is longer than for blue light.

 

Chromatic aberration in lenses
The simple refracting telescope shows the effect of chromatic aberration

The film above (from simple refracting telescope) shows an image made with simple lenses, rather than achromatic lenses. the effects of chromatic aberration are evident.

Links and further information

  • Chromatic dispersion, rainbows and Alexander's dark band
  • Colour of the sky
  • Lenses and images
  • Microscopes and magnifiers
  • Newton's prisms
  • Reflecting Newtonian telescope
  • Refracting telescope
  • Snells law and refraction
  • The multimedia tutorial Geometrical Optics also has a longer list of support pages
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