1. The focal length of a bi-convex thin lens is 10 cm. To a real image with magnification of -2, what is the object distance p? What is the image distance? Is it upright or inverted?
2. The focal length of a bi-convex lens is 10 cm. The focal length of a convex-concave thin lens is -20 cm. If placing them in parallel and in close contact, what is the compound focal length?