Question

Sudha finds out that the sharp image of the window pane of her
science laboratory is formed at a distance of 15 cm from the lens.
She now tries to focus the building visible to her outside the window
instead of the window pane without disturbing the lens. In which
direction will she move the screen to obtain a sharp image of the
building?

Answer 1

Dear Student,

In order to obtain a sharp image of the building outside the window Sudha should move the screen towards the mirror and keep the lens fixed (we can also do it the other way around). As the building is far away we can assume that the incident light rays would be parallel to each other and behave as coming from infinity.

The focal length of the lens would be approximately equal to 15cm as the original distance between the lens and screen is 15cm when the initial image was formed.

Regards