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

Two transparent media $A$ and $B$ are separated by a plane boundary. The speed of light in those media are $1.5 \times 10^{8} \ m/s$ and $2.0 \times 10^{8} \ m/s$,respectively. The critical angle for a ray of light for these two media is:

On the hypotenuse of a right-angled prism $(30^{\circ}-60^{\circ}-90^{\circ})$ with a refractive index of $1.50$,a drop of liquid is placed as shown in the figure. Light is allowed to fall normally on the short face of the prism. In order for the ray of light to undergo total internal reflection at the hypotenuse,what is the maximum value of the refractive index of the liquid?

$A$ transparent block $A$ having refractive index $\mu_2 = 1.25$ is surrounded by another medium of refractive index $\mu_1 = 1.0$ as shown in the figure. $A$ light ray is incident on the flat face of the block with incident angle $\theta$ as shown in the figure. What is the maximum value of $\theta$ for which light suffers total internal reflection at the top surface of the block?

$A$ well-cut diamond appears bright because

$A$ small bulb is placed at the bottom of a tank containing water to a depth of $\sqrt{7} \; m$. The refractive index of water is $\frac{4}{3}$. The area of the surface of water through which light from the bulb can emerge out is $x \,\pi \; m^{2}$. The value of $x$ is ...............