Question

(a) one –half of a convex lens is covered with a black paper. Will such a lens produce an image of the complete object? Support your answer with a ray diagram.; (b) An object 5 cm high is held 25 cm away from a converging lens of focal length 10 cm.; (i) Draw the ray diagram and; (ii) Calculate the position and size of the image formed.; (iii) What is the nature of the image?(Delhi - 2011)

Answer 1

Answer:

(a) When, the one half of the convex lens is covered with a black paper, the lens will still produces an image of the complete object but the intensity of the image will be reduced on covering with black paper.

The ray diagram will be as follows:

(b) (i) object size= 5cm

Object distance, u = 25 cm

Focal length, f = 10 cm

The ray diagram will be as follows:

(ii) Image distance, v =?

Object distance, u = -25 cm

Image size, h1 = 5cm

Image size, h2=?

Applying the lens formula:

(1/v)-(1/u) = 1/f

1/v -(1/-25) = 1/10

1/v +1/25 = 1/10

1/v = 1/10-1/25

1/v = (25-10)/250

1/v = 15/250

1/v = 3/50

v = 50/3

v = + 16.6 cm

(iii) Nature of the image will be as follows:

Since, v is positive, which means that the image is real

The height of image, h2 is negative, which means that the image is inverted.