Question

(a) Define optical center of a spherical lens.; (b) A divergent lens has a focal length of20 cm. At what distance should an. object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens. Find the size of the image also.; (c) Draw a ray diagram to show the formation of image in above situation.(All India - 2016)

Answer 1

Explanation:

Hope it will help you...

Answer 2

Let us solve for Spherical lens :

Explanation:

(a)optical center

It is center of lens

(b) For concave lens it is given that :

Focal length = 20cm

Height of object = 4 cm

Image distance =10cm

Object distance =?

$1/v-1/u=1/f\\1/(-10)-1/u=1/(-20)\\-1/u=-1/20 +1/10\\-u=20cm \\u=-20cm$

Now, let us find the size of image

$m=v/u\\m=-10/-20\\m=1/2\\m=hi/ho\\1/2=hi/4\\hi=2cm$

The ray diagram is attached below .