Total internal reflection.

1. Ray passes through unrefracted .
2. Ray is bent away from the normal.
3. x is the critical angle. Ray is refracted at 90° .
4. Total internal reflection.

The critical angle is the angle of incidence for which the angle of refraction is 900.

The two conditions necessary for total internal reflection to occur:

1. The angle of incidence must be greater than the critical angle.
2. The light must be travelling from a more dense medium to a less dense medium.

Total internal reflection is used in medicine, periscopes and binoculars.

Internal reflection of 90° prism.

Use: plane mirror
Used in place of mirrors. (mirrors give multiple images)

Use: prismatic binoculars.
Image reversed and inverted.

Use: to correct an inversion which has already occurred in an optical instrument. Image inverted.

Periscope.
Light can be intenally reflected in a rod of glass or perspex.
"light pipe" in fibre optic