Question

Critical angle is that angle of incidence in the denser medium for which the angle of refraction in rarer medium is

• A. $0^{\circ }$
• B. ${60}^{\circ }$
• C. ${90}^{\circ }$
• D. ${180}^{\circ }$

Answer 1

The correct option is C

${90}^{\circ }$

Critical angle is that angle of incidence after which the total internal reflection occurs. The angle of refraction for the critical angle is equal to ${90}^0$.

${\theta }_c=$ Critical angle

Using Snell's law:

$\text{sin}{\theta }_c\times U_R=\text{sin}{90}^{\circ }\times {\mu }_D$

or, $\text{sin}{\theta }_c=\frac{{\mu }_D}{{\mu }_R}$

or, ${\theta }_c={\text{sin}}^{-1}\frac{{\mu }_D}{{\mu }_R}$