I've done what you advised and got out the right focal length as 19.2cm but I don't understan how the problem is based on the image-object swap thing seeing as that isn't covered in our textbook and seeing as the lens is moved not the object or screen. Also I'm confused as to why I also get the...
An object and a screen are fixed at a distance of 80cm apart and a convex lens forms a real image of the object on the screen. When the lens is moved along its axis a distance of 16cm, a real image of the object is again formed on the screen. Find the focal length of the lens and the...