Find the object distances (in terms of f ) for a thin converging lens of focal length f if the image...

Find the object distances (in terms of f ) for a thin converging lens of focal length f if (a) the image is real and the image distance is four times the focal length; (b) the image is virtual and the image distance is three times the focal length. (c) Calculate the magnification of the lens for cases (a) and (b). The lens maker’s equation for a lens with index n1 immersed in a medium with index n2 takes the form