Question

a student obtained a sharp image of a lighted candle on a screen using convex lens..now he wants to focus a distant lamp...in which direction shud the lens b moved for this purpose with respect to the screen to get a sharp image on the screen?justify.....

Answer 1

Given:

A student obtains sharp image of candle on screen using convex lens.
To focus distant lamp , where  the lens should be placed?
The lens should be moved towards screen so that a clear image and sharp image is obtained.

Reason:

When we move lens towards screen, then object moves farther away from lens. Hence we can consider object at infinity , light rays from infinity incident on convex lens, after refraction converge at focus and image is formed there.