Refraction

Total Internal Reflection

For total internal reflection to occur the incident light ray needs to be travelling from a more optically dense medium to a less optically dense medium.

TIR occurs at the boundary between the two different mediums.

The reflection is from inside the material.

All the light is reflected

The reflection occurs inside the optically more dense medium.

The incident ray must be greater than the critical angle.

At the critical angle the refracted ray is 90 degrees to the normal

Total internal reflection is the basis of many useful optical devices eg,

endoscopes

safety reflectors on cars, bicycles etc

Binoculars

Periscopes