This animation shows the change of speed when waves move from air to a more dense medium such as glass (refractive index = 1.5) or diamond (refractive index = 2.42).
A pulse of ten waves in sent into each material.
The speed of light in glass is approximately 0.67 of that in air while in diamond it is only 0.41 of the speed in air. Notice the resulting decrease in wavelength in the two materials.
