An optical fibre ( = 1.72 ) is enclosed by a glass coating ( = 1.50 ). Determine the critical angle for total internal reflection at the fibre-glass interface.

Step-by-step solution

The critical angle _c for total internal reflection at the interface of two media is given by _c = ₂ ₁ , where ₂ is the refractive index of the rarer medium and ₁ is the refractive index of the denser medium. Given ₁ = 1.72 (optical fibre) and ₂ = 1.50 (glass coating). Substituting the values: _c = 1.50 1.72 _c = 150 172 _c = 75 86 _c = ⁻¹ ( 75 86 )