Question

to find the image distance for varying object distances in case of a convex lens of focal length 10 cm in student obtained on a screen a sharp image of a bright object by placing it at 20 CM distance from the lens after that he gradually move the object away from the lens and each time focuses the image on the screen <br />a) in which direction towards or away from the lens does he move the screen to focus the object ?<br />b) how does the size of the image change?<br />c) approximately at what distance does he obtain the image of magnification -1? how does the intensity of image change as the object moves farther and farther away from the lens ?​

Answer 1

1/v=1/u+1/f

this formulae used to calculate the obiect