Question

An object i 5 cm in front of diverging lens (focal length 10 cm). 20 cm behind diverging lens is converging lens (focal length 20 cm). where is the image? is it real or virtual?

Answer 1

Given

focal length of diverging lens is f1 = -10 cm

object distance is s1 = 5 cm

the relation between object distance , image distance and focal length is  

1/s +1/s' = 1/f

1/s1' = 1/f1 -1/s1

1/s1' = -1/10 -1/5

s1' = -3.33 cm

that is the image is formed infront of the lens  

it will act as the object to the converging lens  

the object distance s2 = 20+3.33 = 23.33 cm

focal length of the converging lens is f2 = 20 cm

the image distance is

1/s2' = 1/f2 -1/s2

1/s2' = 1/20 -1/23.33

s2' = 140.120 cm = 1.40120 m

the image is real image and inverted also