An unpolarised light beam of intensity $2 I_{0}$ is passed through a polaroid $P$ and then through another polaroid $Q$ which is oriented in such a way that its passing axis makes an angle of $30^{\circ}$ relative to that of $P$. The intensity of the emergent light is.

$n$ polarizing sheets are arranged such that each makes an angle $45^{\circ}$ with the preceding sheet. An unpolarized light of intensity $I$ is incident on this arrangement. The output intensity is found to be $\frac{I}{64}$. The value of $n$ will be:

Three polarising sheets are placed co-axially. The pass axes of polaroids $2$ and $3$ make angles of $30^{\circ}$ and $90^{\circ}$ respectively with the pass axis of polaroid $1$. If $I_0$ is the intensity of unpolarised light entering sheet $1$,what is the intensity of the light emerging from sheet $3$? $(\cos 30^{\circ}=\sqrt{3} / 2, \cos 90^{\circ}=0, \cos 60^{\circ}=1 / 2)$

Two Nicol prisms are inclined at an angle of $60^o$ to each other. What percentage of the incident unpolarized light passes through the system?

Two polaroids have their polarizing directions parallel so that the intensity of a transmitted light is maximum. The angle through which either polaroid must be turned if the intensity is to drop by one-half is.....$^o$

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