$A$ wide container is filled with water $\left(\mu=\frac{4}{3}\right)$ up to a height of $1 \ m$. Find the diameter of the disc at the top of the water surface from which light is coming out.

$A$ glass prism whose cross-section is an isosceles triangle stands with its (horizontal) base in water; the angles that its two equal sides make with the base are each $\theta$. An incident ray of light,above and parallel to the water surface,is totally internally reflected at the glass-water interface and subsequently re-emerges into the air. Take the refractive indices of glass and water to be $\frac{3}{2}$ and $\frac{4}{3}$,respectively. The maximum value of $\cos\theta$ is:

$A$ point source of light is placed $4 \; m$ below the surface of water of refractive index $5/3$. The minimum diameter of a disc which should be placed over the source on the surface of water to cut-off all light coming out of water is ... $m$.

$A$ ray of light passes from a denser medium to a rarer medium at an angle of incidence $i$. The reflected and refracted rays make an angle of $90^{\circ}$ with each other. The angles of reflection and refraction are respectively $r$ and $r^{\prime}$. The critical angle is given by:

$A$ well-cut diamond appears bright because

The refractive index of glass is $1.5$ and that of water is $1.33$. The critical angle for a ray of light going from glass to water is