Light travels in two media $A$ and $B$ with speeds $1.8 \times 10^8 \ m/s$ and $2.4 \times 10^8 \ m/s$ respectively. Then the critical angle between them 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:

In the diagram shown,a ray of light is incident on the interface between medium $1$ and $2$ at an angle slightly greater than the critical angle. The light undergoes total internal reflection at this interface. After that,the light ray falls on the interface of medium $1$ and $3$,and again it undergoes total internal reflection. Which of the following relations should hold true?

Calculate the critical angle for a glass-air surface,if a ray of light incident in air on the glass surface is deviated by $15^{\circ}$ when the angle of incidence is $45^{\circ}$. (in $^{\circ}$)

White light is incident on the interface of glass and air as shown in the figure. If only green light undergoes total internal reflection,then the rays in the air are:

$A$ light ray falls on a glass surface of refractive index $\sqrt{3}$,at an angle of $60^{\circ}$. The angle between the refracted and reflected rays would be ....... $^o$.