(i) Define focal length of a spherical lens. (ii) A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens? Find the size of the image also. (iii) Draw a ray diagram to show the formation of image in the above situation.

(i) Define focal length of a spherical lens. (ii) A divergent lens ha

1.	(i) Define focal length of a spherical lens. (ii) A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens? Find the size of the image also. (iii) Draw a ray diagram to show the formation of image in the above situation.
Answer» Solution :(i) Focal length of a spherical lens: DISTANCE between optical CENTRE of focus of the lens. (ii) f=-30 , u= ? ,`h_(1)=5cm, h_(2)=?,v=-15cm` `1/f=1/v-1/u` `implies1/u=1/v-1/f` `impliesu=(VF)/(f-v)=((-15cm)xx(-30cm))/(-30cm-(-15cm))` `=-30cm` `m=v/u=(h_(2))/(h_(1))` `impliesh_(2)=v/uxxh_(1)` `=(-15cm)/(-30cm)xx5cm=2.5cm`