Sudha finds that a sharp image of the windowpane of her science laboratory is formed from the lens at a distance of 15 cm. Then she tries to focus on the building, which is visible to her outside the window, instead of the windowpane without disturbing the lens. To obtain a sharp image of the building, in which direction will she move the screen? What is the optimal focal length of this lens?

Sudha finds that a sharp image of the windowpane of her science laboratory is formed from the lens at a distance of 15 cm. Then she tries to focus on the building, which is visible to her outside the window, instead of the windowpane without disturbing the lens. To obtain a sharp image of the building, in which direction will she move the screen? What is the optimal focal length of this lens?