Before starting this problem, check out the section on the thin-lens formula and the magnification formula. Check out the Summary of Sign Conventions for Lenses in the text.
A 5.60-cm tall pencil is placed 10.6 cm in front of a lens. An image is formed 4.10 cm on the opposite side of the lens from the object. What is the focal length of the lens?
A 3.90-cm tall pencil is placed 11.4 cm in front of a lens. An image is formed 4.40 cm on the same side of the lens as the object. What is the focal length of the lens?
A 5.20-cm tall pencil is placed 12.3 cm in front of a lens. The focal length of the lens is +29.5 cm. What is the image distance (with proper sign)?