Question

Explain why the emergent rays parallel to the incident ray when a light travels through a glass slab?

Answer 1

The glass slab has two parallel surfaces...and by the principle of reversibility..in second surface

I=r and r=i

Answer 2

The extent of bending of the ray of light at the opposite parallel faces of the rectangular glass slab is equal and opposite. that is why the ray emerges parallel to the incident ray.