Question

A real image exactly 1/5th the size of the object is formed at a distance of 18cm from lens. Find the focal length of the lens

Answer 1

Answer:

3cm

Explanation:

formula for magnification in lens is

m= f/(f+u) =v/u =(f-v)/f

here we have u=-18

m=-1/5 (-ve as it is real)

then -1/5 = f/(f-18)

on solving u get 3 cm