If $\mu_1$ and $\mu_2$ are the refractive indices of the materials of core and cladding of an optical fibre,then the loss of light due to its leakage can be minimised by having

Assertion $(A)$: Propagation of light through an optical fibre is due to total internal reflection taking place at the core-clad interface.
Reason $(R)$: Refractive index of the material of the core of the optical fibre is greater than that of air.

Light enters at an angle of incidence $\alpha$ into a transparent rod of refractive index $n.$ For what value of the refractive index of the material of the rod will the light,once entered into it,not leave it through its lateral face,regardless of the value of the angle of incidence $\alpha$?

Two transparent media $A$ and $B$ are separated by a plane boundary. The speed of light in those media are $1.5 \times 10^{8} \ m/s$ and $2.0 \times 10^{8} \ m/s$,respectively. The critical angle for a ray of light for these two media is:

$A$ glass prism of refractive index $1.5$ is immersed in water (refractive index $4/3$) as shown in the figure. $A$ light beam incident normally on face $AB$ undergoes total internal reflection at face $BC$.

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