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

The tourmaline crystal:

An optically active compound:

Two polaroids are placed in the path of an unpolarised light beam of intensity $I_0$ such that no light is emitted from the second polaroid. If a third polaroid,whose polarisation axis makes an angle $\theta$ with that of the first polaroid,is placed between the polaroids,then the intensity of light emerging from the last polaroid is

The graph showing the dependence of intensity of transmitted light on the angle between polariser and analyser is ($I_0$ is intensity of plane polarised light)

The phenomenon of polarization shows that light has ......... nature.