Question

To find the image distance for varying object distances in case of a convex lens of focal length 1.5 cm, a student obtains on a screen a sharp image of a bright object by placing it at 20 cm distance from the lens. After that he gradually moves the object away from the lens and each time focuses the image on the screen. 

(i) In which direction-towards or away from the lens does he move the screen to focus the object ? 

(ii) How does the size of image change ? 

(iii) Approximately at what distance does he obtain the image of magnification -1 ? 

(iv) How does the intensity of image change as the object moves farther and farther away from the lens ?

Answer 1

(i) Towards the lens.

(ii) Size decreases gradually.

(iii) Nearly 30 cm from the lens.

(iv) Intensity of the image gradually increases.