Question

A paraxial ray is incident on a thin convex lens (surrounded by air) and it makes an angle α with principal axis. This ray is incident on lens at a distance h above principal axis. The emergent paraxial ray makes an angle β with principal axis as shown. Then the magnitude of focal length of lens is -

Answer 1

Correct option: (C)

Explanation:

( for paraxial rays α is very small) 

or u = -h / α , similarly v = h / β

substituting values of u and v in