Question

An optical fiber ($\mu =1.72$) has a coating of glass ($\mu =1.5$). The critical angle for total internal reflection is

• A. ${sin}^{-1}\left(\frac{75}{86}\right)$
• B. ${sin}^{-1}\left(\frac{86}{75}\right)$
• C. ${sin}^{-1}\left(0.8\right)$
• D. ${sin}^{-1}\left(0.82\right)$

Answer 1

The correct option is A ${sin}^{-1}\left(\frac{75}{86}\right)$

The critical angle for total internal reflection is given as $sin{\theta }_c=\frac{{\mu }_2}{{\mu }_1}$, where ${\mu }_1$ is the refractive index of the denser medium.
Thus we get

$sin{\theta }_c=\frac{1.5}{1.72}$

or ${\theta }_c=si{n}^{-1}\frac{75}{86}$.