Light is incident from a medium into air at two possible angles of incidence $(A) \ 20^o$ and $(B) \ 40^o$. In the medium,light travels $3.0 \ cm$ in $0.2 \ ns$. The ray will

Critical angle of incidence for a pair of optical media is $45^{\circ}$. The refractive indices of the first and second media are in the ratio:

Which of the following is not due to total internal reflection?

Light is incident normally on face $AB$ of a prism as shown in the figure. $A$ liquid of refractive index $\mu$ is placed on face $AC$ of the prism. The prism is made of glass of refractive index $\frac{3}{2}$. The limit of $\mu$ for which total internal reflection takes place on face $AC$ is

The critical angle for diamond (refractive index $= 2$) is........$^o$

The figure shows a transparent block of side lengths $a$ and $a$. The third dimension of the block is negligible. $A$ point source $S$,which can emit light in all directions,can move inside the block. It is desired that no light from $S$ should pass through the segment $AB$. The region in which $S$ must be present to satisfy this condition is shown by the shaded region. Choose the correct option.