HC Verma Chapter 18 Problem 70 – Plane glass sheet – zero power

Given

Object at u=-30 cm, image formed at v=-30 cm (same depth, virtual)

Find

Focal length

Formula

1/f = 1/v – 1/u = 1/(-30) – 1/(-30) = 0

Solution

f = infinity (zero power)

Answer

f = infinity (plane glass, no optical power)

Diagram / Concept

Plane parallel glass does not alter vergence of paraxial rays

Notes

Only lateral displacement occurs for oblique incidence