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

$A$ ray of light is incident on one face of a $90^{\circ}$ prism and undergoes total internal reflection at the glass-air interface. If the angle of incidence is $45^{\circ}$,then the refractive index $n$ is:

What is total internal reflection?

$A$ small bulb is placed at the bottom of a tank containing water to a depth of $80 \, cm$. What is the area of the surface of water through which light from the bulb can emerge out? The refractive index of water is $1.33$. (Consider the bulb to be a point source.)

Consider the ray diagram for the refraction given below. The maximum value of angle $\theta$ for which the light suffers total internal reflection at the vertical surface is:

Consider telecommunication through optical fibres. Which of the following statements is not true?