Question

An optical fibre $(\mu =1.72)$ is surrounded by a glass coating $(\mu =1.50)$. Find the critical angle for total internal reflection at the fibre-glass interface.

Answer 1

For calculation of critical angle.

$\frac{\sin i}{\sin r}=\frac{{\mu }_2}{{\mu }_1}\Rightarrow \frac{\sin C}{\sin 90}=\frac{15}{1.72}=\frac{75}{86}$

$\Rightarrow C={\sin }^{-1}\left(\frac{75}{26}\right)$