Ray Optics And Optical Instruments

A convex lens has its radii of curvature equal. The focal length of the lens is . If it is divided vertically into two identical plano-convex lenses by cutting it, then the focal length of the plano-convex lens is the refractive index of the material of the lens

A thin converging lens of focal length forms the image of an object on a screen placed at a distance of from the lens. The screen is moved closer to the lens by a distance of . The distance through which the object has to be shifted, so that its image on the screen in sharp again is