Given a double-convex thin lens with refractive index 1.5 , assume that one side of the lens is filled with air (n₁ =1) and the other side is filled with water (n₂=1.33). The radii of curvature of the surface of the lens are 10 cm and 15 cm, respectively. Calculate the two focal lengths. Ans. 16.3 cm,21.7 cm