$A$ light ray from air is incident (as shown in the figure) on the lateral surface of a glass fiber (refractive index $\mu = 1.5$) at an angle of incidence of $60^o$, such that it undergoes total internal reflection. How much time would it take for the light to traverse the straight fiber of length $L = 1 \ km$ (in $\mu s$)?

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:

Assertion: The refractive index of diamond is $\sqrt{6}$ and that of liquid is $\sqrt{3}$. If the light travels from diamond to the liquid,it will be totally internally reflected when the angle of incidence is $30^{\circ}$.
Reason: $\mu = \frac{1}{\sin C}$,where $\mu$ is the refractive index of diamond with respect to the liquid.

$A$ point source of light $S$ is placed at the bottom of a vessel containing a liquid of refractive index $\mu = 5/3$. $A$ person is viewing the source from above the surface. There is an opaque disc $D$ of radius $r = 1\, cm$ floating on the surface of the liquid. The centre of the disc lies vertically above the source $S$. The liquid from the vessel is gradually drained out through a tap. The maximum height $h$ of the liquid for which the source cannot be seen at all from above is: (in $, cm$)

Light travels a distance '$x$' in time '$t_0$' in air and '$4x$' in time '$t_1$' in another denser medium. The critical angle for this medium is

The wavelengths of given light waves in air and in a medium are $6000 \ Å$ and $4000 \ Å$ respectively. The critical angle is