# Let the refractive index of a denser medium with respect to a rarer medium be $n_{12}$ and its critical angle be $\theta C$ . At an angle of incidence A when light is travelling from denser medium to rarer medium, a part of the light is reflected and the rest is refracted and the angle between reflected and refracted rays is 908. Angle A is given by :

$\begin{array}{1 1} (1)\;\large\frac{1}{\cos ^{-1} (\sin \theta _C)} \\ (2)\;\large\frac{1}{\tan ^{-1} (\sin \theta _C)} \\ (3)\;\cos ^{-1} (\sin \theta_C) \\ (4)\;\tan^{-1} (\sin \theta_C) \end{array}$