• # question_answer A ray of light AO in vacuum is incident on a glass slab at angle $60{}^\circ$ and refracted at angle $30{}^\circ$ along OB as shown in the figure. The optical path length of light ray from A to B is: [JEE Main 10-4-2019 Morning] A) $2a+2b$ B) $2a+\frac{2b}{3}$ C) $\frac{2\sqrt{3}}{a}+2b$                 D) $2a+\frac{2b}{\sqrt{3}}$

From Snell's law $1.sin60{}^\circ =\mu sin30{}^\circ$             $\Rightarrow \mu =\sqrt{3}$ Optical path$=AO+\mu (OB)$ $=\frac{a}{\cos {{60}^{o}}}+\sqrt{3}\frac{b}{\cos {{30}^{o}}}$$=2a+2b$