State two common applications of total internal reflection in modern technology or medicine.

Describe the two physical conditions required for total internal reflection to occur at a boundary.

A light ray travels inside a glass block and is incident on the flat boundary with air at point $P$, as shown in the diagram.

Draw on this

The angle of incidence at $P$ is $42^{\circ }$. The critical angle of this glass is $38.8^{\circ }$. Describe the path of the light ray after it reaches point $P$.

State the equation linking critical angle ($c$) and refractive index ($n$).

Calculate the refractive index of this glass block. Give your answer to 3 significant figures.