Prove that in a glass slab the incident ray is parallel to the emergent ray

Question

Prove that in a glass slab incident ray is parallel to the emergent ray

Answer 1

By using Snell theorem of refraction,

n21 = sin i / sin r

n21 = 1 / n12

n12 = sin r / sin e

n21 = sin e / sin r

sin i / sin r = sin e / sin r

Thus,  sin i = sin e

Therefore, Incident ray is parallel to emergent ray.