If the critical angle for total internal reflection from a medium to vacuum is $30^o$,the velocity of light in the medium is

The speed of light in two media $c_1$ and $c_2$ are $1.5 \times 10^8 \ m/s$ and $2 \times 10^8 \ m/s$ respectively. If the light undergoes total internal reflection,the critical angle between the two media is

Assertion $(A)$: Optical fibres are widely used in communication networks. Reason $(R)$: Optical fibres are small in size,light in weight,flexible,and there is no scope for interference in them.

$A$ light ray falls on a glass surface of refractive index $\sqrt{3}$,at an angle of $60^{\circ}$. The angle between the refracted and reflected rays would be ....... $^o$.

White light is incident on the interface of glass and air as shown in the figure. If only green light undergoes total internal reflection,then the rays in the air are:

$A$ parallel beam of light is incident on a glass prism in the shape of a quarter cylinder of radius $R=0.05 \ m$ and refractive index $n=1.5$,placed on a horizontal table as shown in the figure. Beyond the cylinder,a patch of light is found whose nearest distance $x$ from the cylinder is