An optical fiber has a water core (n=1.33) and a fluoropolymer cladding (n=1.20). For a light ray already propagating inside the core, what is the largest angle the ray may make with the fiber axis (measured inside the core) if it is to remain guided by total internal reflection at the core–cladding interface?
a) 35∘
b) 64∘
c) 26∘
d) 42∘