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? What is the approximate focal length of this lens?

Answer 1

The image of the window pane is formed at a distance of 15 cm from the lens. The building which acts as an object is outside the window so it must be away from the window pane, it means the distance of the object is increased from the lens. When the object distance is increased, the image distance is decreased and the image gets closer to focus. Therefore, the screen must be moved towards the lens to obtain the sharp image of the building.

The approximate value of the focal length is 15 cm, but to get the exact value, the given data is insufficient.