Polaroid:
Polarised is a cheap and simple method to obtain plane polarised light. This is a large sized film which is kept between two glass plates. To prepare this film, very small sized crystals of quinine or sulphate or herpethite are set on the sheet of Nitro-cellulose in such a way that their optic axes may remain parallel to each other. These crystals are strong dichroic which absorb one of two refracted rays completely and the second is emerged which is plane polarised. Every Polaroid has its characteristic direction which is known as ‘Polarising Direction’. In figure it is shown by parallel lines.
When beam of ordinary light is incident on a Polaroid, the vibrations parallel to its polarising direction, are emerged and those at right angles to above axis are absorbed. Thus the light emerged from the polaroid is plane polarised. To insure the polarisation by polaroid, it is checked by another Polaroid. As shown in figure, second polaroid is placed on the first one and the intensity of light passing from second polaroid. When second polaroid i. e., the analyser is related about the direction of propagation, the intensity of direction of propagation, the intensity of light is found maximum when the polarising directions of both polaroids are parallel to each other [Figure] and intensity is found minimum (about zero) when polarising directions are perpendicular to each other [Figure]. These observations prove that the light emerged from first polaroid is plane polarised.
