Question

An object of height 4.0 cm is placed at a distance of 30 cm from the optical centre‘O’ of a convex lens of focal length 20 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’ and principal focus ‘F’ on the diagram. Also find the approximate ratio of size of the image to the size of the object.(All India - 2018)

Answer 1

Answer:

here is your answer ......

Answer 2

The position and size of the image formed is :

• h = 4cm , u = (30cm) , f = 20cm

• Lens formula,

1/v - 1/u = 1/f

• Using these formula, we'll find

 image distance

 1/v - 1/(-30) = 1/20

  1/v = 1/60

  v = 60 cm

• Position of image is 60 cm from optical centre on right side of lens

• We know that magnification of lens is given as :

m = (v/u) = h'/h

• Therefore,

h'/h = (v/u)

h' = (v/u)×h

   = -(60/30)×4

   = -8 cm

• The approximate ratio of size of the image to the size of the object =

|h'/h|= |-8 / 4| = 2