Question

A5 cm object is 18.0 cm from a convex lens, which has a focal length of 10.0 cm.

Answer 1

Explanation:

We have,

Height of object is 5 cm

Object distance from a convex lens is 18 cm

Focal length of convex lens is 10 cm

i.e. h = 5 cm

u = -18 cm

f = +10 cm

Let v is distance of the image from the lens. Using lens formula :

$\dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u}\\\\\dfrac{1}{v}=\dfrac{1}{f}+\dfrac{1}{u}\\\\\dfrac{1}{v}=\dfrac{1}{10}+\dfrac{1}{(-18)}\\\\v=22.5\ cm$

The magnification of lens is :

$m=\dfrac{v}{u}=\dfrac{h'}{h}$, h' is height of the image

$\dfrac{v}{u}=\dfrac{h'}{h}\\\\h'=\dfrac{vh}{u}\\\\h'=\dfrac{22.5\times 4}{(-18)}\\\\h'=-5\ cm$

h' = -5.00 cm (in three significant figures)