Unpolarized light falls on two polarizing sheets placed one on top of the other. What must be the angle between the characteristic directions of the sheets if the intensity of the final transmitted light is one-third the maximum intensity of the first transmitted beam.......$^o$

In the propagation of light waves,the angle between the direction of vibration and the plane of polarization is ....$^o$.

Which of the following statements indicates that light waves are transverse?

Three identical polaroids $P_1, P_2$ and $P_3$ are placed one after another. The pass axis of $P_2$ and $P_3$ are inclined at an angle $60^{\circ}$ and $90^{\circ}$ with respect to the axis of $P_1$. The source has an intensity $I_0$. What is the intensity of transmitted light through $P_3$? $\left(\cos 60^{\circ}=0.5, \cos 30^{\circ}=\frac{\sqrt{3}}{2}\right)$

The intensity of transmitted light when a polaroid sheet is placed between two crossed polaroids at $22.5^{\circ}$ from the polarization axis of one of the polaroids is (where $I_0$ is the intensity of polarized light after passing through the first polaroid):

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