A transparent solid cylindrical rod has a refractive index of $\frac { 2 } { \sqrt { 3 } }$. It is surrounded by air. A light ray is incident at the mid point of one end of the rod as shown in the figure. The incident angle $\theta$ for which the light ray grazes along the wall of the rod is (1) $\sin ^ { - 1 } \left( \frac { 1 } { 2 } \right)$ (2) $\sin ^ { - 1 } \left( \frac { \sqrt { 3 } } { 2 } \right)$ (3) $\sin ^ { - 1 } \left( \frac { 2 } { \sqrt { 3 } } \right)$ (4) $\sin ^ { - 1 } \left( \frac { 1 } { \sqrt { 3 } } \right)$
A transparent solid cylindrical rod has a refractive index of $\frac { 2 } { \sqrt { 3 } }$. It is surrounded by air. A light ray is incident at the mid point of one end of the rod as shown in the figure. The incident angle $\theta$ for which the light ray grazes along the wall of the rod is\\
(1) $\sin ^ { - 1 } \left( \frac { 1 } { 2 } \right)$\\
(2) $\sin ^ { - 1 } \left( \frac { \sqrt { 3 } } { 2 } \right)$\\
(3) $\sin ^ { - 1 } \left( \frac { 2 } { \sqrt { 3 } } \right)$\\
(4) $\sin ^ { - 1 } \left( \frac { 1 } { \sqrt { 3 } } \right)$