A cross section of a light pipe made of a glass fibre of refractive index 1.68 . The outer covering of the pipe is made of material of refractive index 1.44 . What is the range of the angles of incident rays with the axis of pipe for which the total reflection inside the pipe takes place .

Question

$\begin{array}{1 1} i < 60^{\circ} \\ i > 60 ^{\circ} \\ i < 31^{\circ} \\ i > 31^{\circ} \end{array}$