Question

how can we say that focal length of the glass slab is infinity​

Answer 1

Answer:

hope it help

The emergent ray in the rectangular glass slab is parallel to the incident ray so the focal length of the glass slab is infinite. As the power of lens is reciprocal to the focal length so the power of a glass slab cannot be defined.

Answer 2

Answer:

Focal length of a glass slab is infinity.

Explanation :

Power of a glass slab is zero.

Focal length is reciprocal of power

So, focal length =1/0=infinity