Refraction is the change in direction of a wave, at an interface between two media that creates a change in speed. If we consider light then the media could be air and glass. The light travels _____ in the glass than in air.
When a ray of light enters a glass block at an angle to the interface (edge) it is bent _____ the normal. When rays leave a glass block they bend _____ the normal. We have seen that the bigger the angle of incidence then the more the ray is refracted (bent)
We have also seen that some of the light is also reflected back at the interface. There is a critical angle at which light is no longer refracted, but instead all of it reflected back inside the block. The critical angle for glass / air is approx. 43°.
This is called Total Internal Reflection and has been used in many practical ways, through the use of optical fibres and prisms.