Total internal reflection of light is possible when light enters from

$A$ small coin is resting on the bottom of a beaker filled with liquid. $A$ ray of light from the coin travels up to the surface of the liquid and moves along its surface. How fast is the light travelling in the liquid?

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

$A$ ray of light propagates from glass (refractive index $= 3/2$) to water (refractive index $= 4/3$). The value of the critical angle is:

The figure shows a mixture of blue,green,and red colored rays incident normally on a right-angled prism. The critical angles of the material of the prism for red,green,and blue are $46^{\circ}$,$44^{\circ}$,and $43^{\circ}$ respectively. The arrangement will separate:

$A$ ray of light enters from a rarer to a denser medium. The angle of incidence is $i$. Then the reflected and refracted rays are mutually perpendicular to each other. The critical angle for the pair of media is