'Mirage' is a phenomenon due to

$A$ material is embedded between two glass plates. The refractive index $n$ of the material varies with thickness as shown in the figure. The maximum incident angle (in degrees) on the material for which the beam will pass through the material is

$A$ fish is a little below the surface of a lake. If the critical angle is $49^\circ$,then the fish could see things above the water surface within an angular range of $\theta^\circ$ where

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.

White light is incident on the interface of glass and air as shown in the figure. If green light is just totally internally reflected,then the emerging ray in air contains:

$A$ light ray is incident perpendicularly to one face of a $90^{\circ}$ prism and is totally internally reflected at the glass-air interface. If the angle of incidence at the interface is $45^{\circ}$,we conclude that the refractive index $n$ is: