Question

an object of hieght 4cm is placed at 40cm from concave lens of focal length 20cm . calculate the position of the image and size of the image.


plz solve this​

Answer 1

Given that - height of object ( O ) = 4 cm

distance of object = -40 cm

Focal length of lens = -20 cm

To find --) position of image = ?

Size or height of image = ?

As by lens formula , we came to knew that ...

1 / F = 1 / V - 1 / U

1 / -20 = 1 / V - ( 1 / -40 )

1 / -20 = 1 / V + 1 /40

1 / V = (1 / -20 ) - 1 / 40

1 / V = ( -2 - 1 ) / 40 = - 3 / 40

V = -40 / 3 = -13.3 cm

as per lens maginification formula ,

M = V / U = I / O

- 13.3 / - 40 = I / 4

I = (13 .3 x 4 ) / 40 = 1.33 cm

hence the position of image is 13.3 cm

and size of image is = 1.33 cm