If the critical angle for total internal reflection from a medium to vacuum is $30^{\circ}$,then the velocity of light in the medium is:

In an optical fibre, the core and cladding are made with materials of refractive indices $1.5$ and $1.414$ respectively. To observe total internal reflection, what will be the range of the incident angle with the axis of the optical fibre?

$A$ light ray falls on a square glass slab as shown in the diagram. The index of refraction of the glass,if total internal reflection is to occur at the vertical face,is equal to

$A$ ray of light is incident on the hypotenuse of a right-angled prism after travelling parallel to the base inside the prism. If $\mu$ is the refractive index of the material of the prism, the maximum value of the base angle for which light is totally reflected from the hypotenuse is

Three transparent media of refractive indices $\mu_1, \mu_2, \mu_3$,respectively,are stacked as shown below. $A$ ray of light follows the path shown. No light enters the third medium. Then,

$A$ fish looking from within water sees the outside world through a circular horizon. If the fish is $\sqrt{7} \ cm$ below the surface of water,what will be the radius of the circular horizon in $cm$?