Question

A double Convex Lens has to surfaces of equal Radii 'R' and
Refractive index n = 15. Find the Focal Length 'f'.​

Answer 1

Answer Explanation:

Given: Radius of Curvature R1 = R2 = R

Refractive Index (n) = 1.5

To Find: Focal Length of the Lens (f)

Lens makers formula ½ = (n-1) [1/R1 – 1/R2]

For Double Convex Lens, R1 is Positive, R2 is –Negative

∴ 1/f = (n-1) [1/R1 – 1/R2]

= (1.5 - 1) [1/R – (-1/R)] = 0.5 [1/R + 1/R] = 0.5 x 2/R

= 1/f = 1/R

= f = R

∴ Focal Lenght of Lens = Radius of Curvature of Surfaces.

Answer 2

Answer:

F=1/2 is the solution I got