In the formation of a primary rainbow,the sunlight rays emerge at minimum deviation from a raindrop after:

The refractive index of water in a biology laboratory tank varies as $1.33 + 0.002 / \lambda^2$,where $\lambda$ is the wavelength of light. Small pieces of organic matter of different colours are seen at the bottom of the tank using a travelling microscope. Then,the image of the organic matter appears

In the figure below,$PQRS$ denotes the path followed by a ray of light as it travels through three media in succession. The absolute refractive indices of the media are $\mu_1, \mu_2$ and $\mu_3$,respectively. (The line segment $RS$ in the figure is parallel to $PQ$). Then,

White light consists of wavelengths ranging from $480 \,nm$ to $672 \,nm$. What will be the wavelength range when white light is passed through glass of refractive index $1.6$?

$A$ ray of light strikes a glass plate at an angle of $60^o$. If the reflected and refracted rays are perpendicular to each other,the index of refraction of the glass is:

An infinitely long cylinder of radius $R$ is made of an unusual exotic material with refractive index $-1$ (See figure). The cylinder is placed between two planes whose normals are along the $y$-direction. The center of the cylinder $O$ lies along the $y$-axis. $A$ narrow laser beam is directed along the $y$-direction from the lower plate. The laser source is at a horizontal distance $x$ from the diameter in the $y$-direction. Find the range of $x$ such that light emitted from the lower plane does not reach the upper plane.