Question

The image of an object formed by a convex lens is of the same size as the object. If the image is formed at a distance of 40 cm, find the focal length of the lens. At what distance from the lens is the object placed?

Answer 1

only one condition is possible when height of object and height of the image is equal when object placed at C then image also form at C here image distance is mentioned 40 cm then object also at -40 cm and C=2F , then F is 20 cm

Answer 2

Answer:

Same size of image is formed by a convex lens only when the object is placed at a distance u=2f from the optical center and image is also formed at distance 2f on other side of lens.

2f=40 cm

f=20 cm

P= 100/f (in cm)

  =100/20

  =+5 D

H.P.