Question

. A student using a convex lens of focal length 20 cm, formed image of an object placed in front of

the lens on one side a screen placed on the other side of the lens. He noted the following reading

for object distance (u) and image distance (v) from lens.

S.No 1 2 3 4 5 6

u (cm) 60 45 40 32 35 15

v (cm) 30 36 45 53 25 10

Without using lens formula, comment, which of these observations are wrong. Justify your


Pls fast tomm exm

Answer 1

This question was asked in my exam which happened today.

Can i know where u got this question from?

It would be really helpful

Answer 2

Answer:

u = 40 v = 45

Explanation:

When u = 40

v = 40

40 is the length which is twice the focal length. At twice the focal length the image is also produced at twice the focal length. Hence, the reading u = 40 v = 45 is wrong.

When an object is placed between the focal length and twice the focal length the image is produced at a distance greater than twice the focal length.

When an object is placed between the focal length and the lens the image is produced on the same side of the lens, is virtual, erect and enlarged.