A lens is a transparent optical medium bounded by two surfaces; at least one of which should be spherical. Considering image formation by a single spherical surface successively at the two surfaces of a lens, lens maker's formula is obtained. It is useful to design lenses of desired focal length using surfaces of suitable radii of curvature. This formula helps us obtain a relation between u,v and f for a lens. Lenses form images of objects and they are used in a number of optical devices, for example microscopes and telescopes.
(i) An object AB is kept in front of a composite convex lens, as shown in figure. Will the lens produce one image? If not, explain.
(ii) A real image of an object formed by a convex lens is observed on a screen. If the screen is removed, will the image still be formed? Explain.
(iii) A double convex lens is made of glass of refractive index 1.55 with both faces of the same radius of curvature. Find the radius of curvature required if focal length is 20‌cm.
OR
(iii) Two convex lenses A and B of focal lengths 15‌cm and 10‌cm respectively are placed coaxially ' d ' distance apart. A point object is kept at a distance of 30‌cm in front of lens A. Find the value of ' d ' so that the rays emerging from lens B are parallel to its principal axis.