Why does a light ray incident on a rectangular glass slab immersed in any medium emerges parallel to itself? Explain using a diagram.
Answer:
When light ray enters denser medium from rarer medium it bends towards the normal. Again, when this ray exists the second medium and enters the first, it ends away from the normal. In this case extent of bending of ray at opposite faces is the same, this is the reason why the emergent ray is parallel to the incident ray.