Question

an image of height 2cm is formed by a convex lens when an object of height 8cm is placed at a distance of 80 cm from it . find the focal length of the lens ... i want full explanation ​

Answer 1

Explanation:

m=h'/h=v/u.(linear magnification of lens)

h'=2cm,h=8cm,u=-80cm

so,h'/h=v/u

h'*u/h=v

That is 2*-80/8=-20cm

by lens formula :

1/v-1/u=1/f

1/-20-(1/-80)=1/f

-4+1/80=1/f (LCM(-20,80)=80)

implies f=80/-3=26.6 cm

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