Question i) Prove that if an object is at a distance of twice the focal length from a converging lens, the image is the same size as the object. Show this using an algebraic method. Possible Answer Must prove u = v 2F = U 2/u + 2/v = u u + v = 2u v=u ii) A small hand-held camera has a convex lens with a focal length of 5cm. The camera is arranged so that by moving the lens in and out, objects from 50cm away to "infinity" (very remote objects like mountains and scenery) can be brought to an exact focus on the film. How many centimeters will the lens have to be moved as the focus is changed from the closest to the farthest object? Possible Answer: Well, F = 5cm U = 50cm No I can't do this, could someone explain it please.