A transparent solid cylindrical rod has a refractive index of ${2 \over {\sqrt 3 }}.$ 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 :
$${\sin ^{ - 1}}\left( {{\raise0.5ex\hbox{$\scriptstyle {\sqrt 3 }$}
\kern-0.1em/\kern-0.15em
\lower0.25ex\hbox{$\scriptstyle 2$}}} \right)$$
$${\sin ^{ - 1}}\left( {{\raise0.5ex\hbox{$\scriptstyle 2$}
\kern-0.1em/\kern-0.15em
\lower0.25ex\hbox{$\scriptstyle {\sqrt 3 }$}}} \right)$$
${\sin ^{ - 1}}\left( {{1 \over {\sqrt 3 }}} \right)$
$${\sin ^{ - 1}}\left( {{\raise0.5ex\hbox{$\scriptstyle 1$}
\kern-0.1em/\kern-0.15em
\lower0.25ex\hbox{$\scriptstyle 2$}}} \right)$$
