Define critical angle and calculate it for glass-air interface. Give two applications of total internal reflection.

The refractive index of glass, $n_{glass} = 1.48$.
The refractive index of air, $n_{air} = 1.00$.
From the diagram, the ray is incident at point X on the glass-air interface. The refracted ray travels along the interface, meaning the angle of refraction in air is $r = 90^\circ$. The angle 'i' is the angle of incidence in the glass.

When light travels from a denser medium (glass) to a rarer medium (air) and the angle of refraction is $90^\circ$, the angle of incidence is the critical angle.
Snell's Law: $n_{glass} \sin i = n_{air} \sin r$

Since $\sin 90^\circ = 1$:

Angle $i$ is $\boxed{42.5^\circ}$.