Question

An object of 8cm height is placed at a distance of 20cm from a convex lens of focal length 40cm. Find the position nature and size of the image

Answer 1

Answer:

position = left side to the lens at 40 cm

size of image is 16 cm

nature of image imaginary magnification m =+2

Explanation:

given

object height = 8 cm

distance of object u = -20 cm

focal length of convex lens f = +40 cm

find :

position v= ? ,nature and size of image

solution

formula for  mirror

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$

put given value

$\frac{1}{40}=\frac{1}{v}-\frac{1}{-20}$

$\frac{1}{v}=\frac{1}{40} -\frac{1}{20}$

$\frac{1}{v}=\frac{1-2}{40}$

$\frac{1}{v}=\frac{-1}{40}$

means

v= -40 cm

position = left side to the lens at 40 cm

magnification formula  

$m=\frac{hight of image}{hight of object} =\frac{v}{u}$

$\frac{height of image}{8}= \frac{-40}{-20}$

$height of image = 16$

size of image is 16 cm

nature of image must be imaginary because magnification +2 positive magnification means that image is imaginary