Two polaroids are oriented with their planes perpendicular to incident light and transmission axis making an angle $30^{\circ}$ with each other. What fraction of incident unpolarised light is transmitted (in $\%$)? $(\cos 30^{\circ} = \sqrt{3} / 2)$

An unpolarised light of intensity $I$ is passed through two polaroids kept one after the other with their planes parallel to each other. The intensity of light emerging from the second polaroid is $\frac{I}{4}$. The angle between the pass axes of the polaroids is (in $^{\circ}$)

Two polaroids are kept crossed to each other. Now one of them is rotated through an angle $45^{\circ}$. The percentage of incident light now transmitted through the system is ......$\%$

$A$ polarized light of intensity $I_{0}$ is passed through another polarizer whose pass axis makes an angle of $60^{\circ}$ with the pass axis of the former. What is the intensity of emergent polarized light from the second polarizer?

The tourmaline crystal:

For the study of the helical structure of nucleic acids,the property of electromagnetic radiation generally used is