Passage 4 (Questions 77-79)
A turnip sits before a thin converging lens, outside the focal point of the lens. The lens is filled with a transparent gel so that it is flexible; by squeezing its ends towards its centre as indicated in figure, you can change the curvature of its front and rear sides.
Suppose that the image must be formed on a card which is at a certain distance behind the lens as shown in the figure, while you move the turnip away from the lens, then you should: