$A$ ray of light travelling in a transparent medium of refractive index $n$ falls on a surface separating the medium from air at an angle of incidence of $45^{\circ}$. For which of the following values of $n$ can the ray undergo total internal reflection?

The phenomenon of reflection of radio waves by the ionosphere is similar to:

$A$ ray of light is travelling from glass to air. (refractive index of glass $= 1.5$). The angle of incidence is $50^{\circ}$. The deviation of the ray is

What is the least radius through which an optical fiber of core diameter $0.05 \, mm$ may be bent (as shown in figure) without serious loss of light (in $, mm$)? The refractive index of the core is $1.6$ and that of cladding is $1.5$.

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.

$A$ light wave travelling linearly in a medium of dielectric constant $4$ is incident on the horizontal interface separating the medium from air. The angle of incidence for which the total intensity of the incident wave will be reflected back into the same medium is (Given: relative permeability of the medium $\mu_{r} = 1$) (in $^{\circ}$)