HC Verma Chapter 18 Problem 9 – Thin lens image – object beyond 2f

Given

Object u=-60 cm, convex lens f=20 cm

Find

Image distance v

Formula

1/v – 1/u = 1/f

Solution

1/v = 1/20 + 1/(-60) … 1/v = 1/f + 1/u = 1/20 + 1/(-60) = 2/60; v = 30 cm

Answer

v = 30 cm (real, inverted)

Diagram / Concept

Object beyond 2f gives real image between f and 2f

Notes

m = v/u = 30/(-60) = -0.5, diminished