Total Internal Reflection

Total internal reflection (TIR) occurs when:

1. Light travels from a denser to a less dense medium.
2. The angle of incidence exceeds the critical angle.

At the critical angle $c$:

$\sin c = \frac{1}{n}$

where $n$ is the refractive index of the denser medium (relative to air/vacuum).

Applications: optical fibres (telecommunications and endoscopes), cat’s eye reflectors, prismatic binoculars, bicycle reflectors.

In optical fibres, light enters at one end and undergoes repeated TIR along the length, allowing signals to travel long distances with minimal loss.