CBSE Class 12-science Answered

a) To distinguish between plane polarised light and partially polarised light , the beam is first allowed to fall on a    polaroid. On rotating the polaroid along the direction of propagation of light, if the intensity changes from maximum to zero minimum twice in one rotation then the light is plane polarised.

On rotating the polaroid if the emergent light shows variation in intensity, but without any zero minimum, then the incident light is partially polarised. If the light incident on the analysing polaroid is partially polarised then the emergent light will never cut off during one rotation of the polaroid.

b) Malus law states that when a completely plane polarised light beam is incident on a polarising sheet , the intensity of light transmitted through the analyser varies as the square of the cosine of the angle between the plane of transmission of the analyser and the plane of the polariser.