Consider the following statements $A$ and $B$. Identify the correct choice in the given answers.
$A$. The refractive index of the extra-ordinary ray depends on the angle of incidence in double refraction.
$B$. The vibrations of light waves acquire one-sidedness for both ordinary and extraordinary rays in double refraction.

What is partially polarised light?

The transverse nature of light was confirmed by the phenomenon of

Two polaroids $A$ and $B$ are placed perpendicularly in the path of a beam of unpolarized light. In between these two,a third polaroid $C$ is placed at an angle of $30^o$ with that of $A$. The percentage of intensity of incident unpolarized light that emerges from $B$ is ........$\%$.

Three linear polarisers are placed coaxially. The transmission axis of the first polariser is at $30^{\circ}$,the second one is at $60^{\circ}$,and the third at $90^{\circ}$ to the vertical,all in the clockwise sense. Each polariser additionally absorbs $10 \%$ of the light. If a vertically polarised beam of light of intensity $I=100 \, W/m^2$ is incident on this assembly of polarisers,then the final intensity of the transmitted light will be close to ................ $W/m^2$.

$A$ polarizer-analyser set is adjusted such that the intensity of light coming out of the analyser is $10 \%$ of the original intensity. Assuming that the polarizer-analyser set does not absorb any light,the angle by which the analyser needs to be rotated further to reduce the output intensity to zero is.....$^o$