As shown in the figure,a light ray $P$ enters a slab at an angle of $60^{\circ}$ with the normal. Inside the slab,the light ray $Q$ undergoes total internal reflection at the vertical face. Find the minimum refractive index of the slab.

$A$ beam of light consisting of red,green and blue colours is incident on a right-angled prism on face $AB$. The refractive indices of the material for the above red,green and blue colours are $1.39, 1.44$ and $1.47$ respectively. $A$ person looking on surface $AC$ of the prism will see

The reason for the shining of an air bubble in water is

On a bright sunny day,a diver of height $h$ stands at the bottom of a lake of depth $H$. Looking upward,he can see objects outside the lake in a circular region of radius $R$. Beyond this circle,he sees the images of objects lying on the floor of the lake. If the refractive index of water is $4/3$,then the value of $R$ is:

$A$ ray of light originates from inside a glass slab and is incident on its inner surface at an angle $\theta$ as shown below. In this experiment,the location $x$ of the spot where the ray hits the screen is recorded. Which of the following correctly shows the plot of variation of $x$ with the angle $\theta$?

$A$ ray is incident from a medium of refractive index $2$ into a medium of refractive index $1$. The critical angle is (in $^{\circ}$)