Detection of plane polarised light:
i. Naked eyes or the polariser alone cannot make distinction between unpolarised light and plane polarised light. To analyse the nature of light, another crystal (analyser) is used.
ii. The tourmaline crystal is used to produce plane polarised light.
iii. If the polariser is rotated in the path of ordinary light, the intensity of the light transmitted from the polariser remains unchanged. It is because in each orientation of the polariser, the plane polarised light is obtained which has vibrations in a direction parallel to the axis of the crystal in that orientation.
iv. If the analyser is rotated in the path of the light transmitted from the polariser, so that the axis of the polariser and the analyser are parallel to each other, then the intensity of light is found to remain unaffected [see figure (a)].
v. If the axis of the polariser and the analyser are perpendicular to each other as shown in figure (b), then the intensity of light becomes minimum.
In this position, the polariser and the analyser are said to be in crossed position.
