Index of refraction of an optical fiber

1. The problem statement, all variables and given/known data
The glass core of an optical fiber has an index of refraction 1.62. The index of refraction of the cladding is 1.47.
What is the maximum angle a light ray can make with the wall of the core if it is to remain inside the fiber?

2. Relevant equations

theta = sin ^-1 (n2/n1)

3. The attempt at a solution
i used the equation and got angel 65.15 which was wrong


Homework Helper
The critical angle is 65 all right, but that is the angle of incidence - measured from a line perpendicular to the surface. The question asks for the angle "with the wall of the core". So you want 90-65.15.

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