A Fiber Optic Is Made by Cladding a Thin Fiber

Multiple Choice

A fiber optic is made by cladding a thin fiber core of refractive index n₁ = 1.45 with a material of refractive index n₂ = 1.38. The numerical aperture of a fiber optic is defined as NA = n_air sin θ_m, where θ_m is the maximum incident angle so that the light ray is totally internally reflected inside the fiber. The NA for the fiber is

A) 0.445.
B) 0.614.
C) 0.645.
D) 0.407.
E) 0.470.