If $n_{21} > 1$,then write the relation between the angle of incidence and the angle of refraction.

In a medium,the speed of a light wave decreases to $0.2$ times its speed in free space. The ratio of relative permittivity to the refractive index of the medium is $x: 1$. The value of $x$ is $...........$ (Given: speed of light in free space $= 3 \times 10^8 \ m \ s^{-1}$ and for the given medium $\mu_r = 1$)

$A$ light ray is incident on a transparent sphere of refractive index $\mu = \sqrt{2}$ at an angle of incidence $i = 45^{\circ}$. What is the total deviation of a ray that enters the sphere,undergoes two internal reflections,and then refracts out into the air (in $^{\circ}$)?

The phase difference between the incident wave and the reflected wave is $180^o$ when a light ray:

The wavelength of light in air and some other medium are respectively ${\lambda_a}$ and ${\lambda_m}$. The refractive index of the medium is:

What are optically denser and optically rarer media?