Question

an object 6 CM in size is placed at 50 cm in front of a convex lens of focal length 30 cm. At what distance from the lens should a screen be placed in order to obtain a sharp image of the object ? Find the nature and size of the image . Also draw labelled ray diagram to show the image formation in this case.

( 5 Marks question )

CBSE board 2019 question paper

Series -JMS/2
Set-3​

Answer 1

Height of object = +6 cm

Object distance = -50 cm

Focal length = +30 cm

Lens formula = 1/f = 1/v - 1/u

                        1/v = 1/f + 1/u

                        1/v = 1/30 - 1/50

                              = 5-3/150

                              = 2/150

                        Image distance = 150/2 = +75.5 cm

                           height of image  =  image distance

                            height of object       object distance

                              h =  75.5 x 6

                                         - 50

                                h = +9.06 cm

       Hence image formed is virtual, erect, and magnified

Answer 2

V= + 75 cm

And nature is. Real inverted. Magnified