Consider the following statements $A$ and $B$ and identify the correct answer:
$A$. Polarised light can be used to study the helical surface of nucleic acids.
$B$. Optical axis is a direction and not any particular line in the crystal.

Indicate the signals used for unpolarised,polarised,and partially polarised light.

An unpolarised beam of light is incident on a group of three polarising sheets arranged such that the angle between the axes of any two adjacent sheets is $30^{\circ}$. The ratio of the intensities of polarised light emerging from the second and third sheets is

$A$ mixture of plane-polarized and unpolarized light falls normally on a polarizing sheet. On rotating the polarizing sheet about the direction of the incident beam,we find that the ratio of maximum to minimum transmitted intensity is $4$. Find the ratio of the intensities $I_P$ and $I_0$,respectively,of the polarized and unpolarized components in the incident beam.

Four polaroids are placed such that the optic axis of each is inclined at an angle of $30^{\circ}$ with the optic axis of the preceding one. If unpolarised light of intensity $I_0$ falls on the first polaroid,the intensity of light transmitted from the fourth polaroid is $[\cos 30^{\circ} = \sqrt{3} / 2]$.

What is partially polarised light?