A plane glass is placed over a various coloured letters (violet, green, yellow, red). The letter which appears to be raised more is

A ray of light passes through four transparent media with refractive index $n_1,n_2,n_3$ and  ${\mathrm{n}}_4$ as shown. The surfaces of all media are parallel

If the emergent ray $DE$ is parallel to incident ray $AB$, then

A transparent solid cylindrical rod has a refractive index of $\frac{2}{\sqrt{3}}.$ It is surrounded by air. A light ray is incident at the mid-point of one end of the rod as shown in the figure.

The incident angle $\theta$ for which the light ray grazes along the wall of the rod is

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