Spark image

Wave speed change

When light waves pass from air into a transparent material such as glass or diamond they slow down. The size of this change of speed depends on the refractive index of the material.The larger the refractive index the bigger the change of speed. Diamond has a higher refractive index (2.42) than glass (1.5) and so the waves slow down more in diamond than they do in glass.

When the waves come out into air they speed up again.
© Keith Gibbs/John Bourne 2008