If a wave passes from air, through a glass block and emerges from the block from the opposite face into air again, the emergent wave will be parallel to the incident wave.
The ray may not emerge on the opposite face as shown below.
In this case we can use Snell's law to find
for example, given
and
If n-glass =1.2 and
The angle of incidence onto the second face is then 90-32.39 = 57.61 degrees.
