Reflection and refraction are not quite as simple as we have stated previously. However, for the purposes of our future discussion we will be able to avoid most of the complications.
There is a complication, related to the intensity of refracted light, that arises in practice. Often, when a beam of light strikes a surface and refracts, there will also be a small amount of reflection from the point of intersection.
An everyday example of this is seeing your reflection when you walk by a store window.
This effect will not play too important a role in our discussion, so this will be our last mention of intensity1.
In many cases, the index of refraction actually depends on the wavelength of the light being considered. One well-known example of this is the splitting of white light into the colours of the rainbow.
The association between wavelength and refractive index is called dispersion.
In our presentation fo lenses, dispersion will be important. For completeness, we list some values of n for glass here.
|nglass as a Function of Wavelength|
Notice that as wavelength increases (as we move from bluer to redder light), n decreases; in essence bluer light is bent more than redder light.