(i) If f =- 0.2 m for a glass lens, what is the power ofthe lens?
(ii) The radii ofcurvature ofthe faces of a double convex lens are 15 cm and 12 cm. Its focal length is 15 cm. What is the refractive index of glass ?
(iii) Refractive index and radii of curvature oftwo equal plana-convex lens are 1.5 and 20 cm respectively. They are placed in a vessel such that their convex surfaces are in contact at centre and oil ofrefractive index 1.7 is filled in them, then what will be the focal length of combination ?

Explanation

P = + 5D , (ii) n=1.5 (iii) `f_(eq) = - 50 cm `