Question

A teacher sets up the stand carrying a convex lens of focal length 15 cm at 42.7 cm mark on the optical bench. He asks four students A, B, C and D to suggest the position of screen on the optical bench so that a distinct image of a distant tree is obtained almost immediately on it. The positions suggested by the students were as : (A) 12.7 cm (B) 29.7 cm (C) 57.7 cm (D) 72.7 cm. The correct position of the screen was suggested by :a) A b) B c) C d) D

Answer 1

Answer:

option A

Explanation:

in convex lens the position of the image always will be less than the focal length. so option A is correct which is 12.7cm(less than focal length).

Answer 2

Answer:

Option C : 57.7cm is correct option .

Explanation:

Given convex lens of Focal length =f=15cm

It is placed at 42.7cm mark on optical bench[position of lens]

When we want the distant object let us say tree to be focused approximately , we get image at focus of convex lens .

Because rays from distant object are parallel rays and they get converged at focus.

Hence position of screen=Distance marked on bench[lens placed] + focal length

=42.7 +15

=57.7cm