For a thin convex glass lens with radius of curvature 20 cm, the focal length is cm. The refractive index n of the material of the lens is 1.5 and it is kept in air. [Hint: for an air-glass lens, -1/u+1/v=(n-1)/R=1/f]

Question

Accepted Answer

(2) 40. Given: a thin convex glass lens with one curved surface of radius R=20 cm, n=1.5, in air. The printed hint fixes the form to use: 1/f=(n-1)/R. Idea: every refracting surface adds (n-1)/R to the power of the lens. Here that term appears once, so the lens is half as strong as a double convex lens of the same radius. 1/f=(1.5-1)/(20)=(0.5)/(20). That is 1/f=1/(40). So the focal length is f=40 cm.

For a thin convex glass lens with radius of curvature 20 cm, the focal length is ______ cm. The refractive index n of the material of the lens is 1.5 and it is kept in air. [Hint: for an air-glass lens, -1/u+1/v=(n-1)/R=1/f]

Step-by-step solution

Why the other options are wrong