A converging lens is symmetric; its curved sides have radii of 50 cm.If the focal length is to be 80 cm, what should the index of refraction be?
A)0
B)0.3
C)0.6
D)1.3
E)1.6

Question

Quizplus · Accepted Answer

The lens maker's equation is:1/f = (n-1)(1/R1 + 1/R2)where f is the focal length, n is the index of refraction, and R1 and R2 are the radii of curvature of the two surfaces.For a symmetric lens, R1 = R2 = R. So, the equation becomes:1/f = (n-1)(2/R)Solving for n, we get:n = 1 + f/2RSubstituting the given values, we get:n = 1 + 80 cm / 2(50 cm) = 1.6

A Converging Lens Is Symmetric; Its Curved Sides Have Radii