In the formation of primary rainbow, the sunlight rays emerge at minimum deviation from rain-drop after

Reason: Internal reflection from water droplet causes dispersion. The final ray is in the backward direction.

Light travels from a medium of refractive index ${\mu }_1$ to another of refractive index ${\mu }_2\left({\mu }_1>{\mu }_2\right)$. For total internal reflection of light, which is NOT true?

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