HC Verma Chapter 18 Problem 72 – Convex lens – image size

Given

Object 6 cm tall, u=-30 cm, f=20 cm

Find

Image height

Formula

1/v = 1/f + 1/u; image height = m x object height

Solution

1/v = 1/20 + 1/(-30) = 1/60; v = 60 cm; m = 60/(-30) = -2; image = 12 cm

Answer

Image height = 12 cm (inverted, real)

Diagram / Concept

Object at 1.5f gives image at 3f with |m|=2

Notes

Object between f and 2f gives magnified real image