We have seen above that a pile of glass plate acts as a polarizer. Suppose that Two such pile of plates are used as shown in fig 6.When the planes of incidence for both the sets are parallel (i.e angle of incidences are at Brewster angle) the output from the second plate will be p polarized light. . Now suppose that the second pile of plate is rotated about the axis X-X' as shown such that the plane of incidence changes for the second set of glass plates.. You will observe that the light intensity will start decreasing and finally when the second plate is rotated by 90 , the output light is zero because for this position the electric field is perpendicular to the plane of incidence and the light will be reflected completely from it. On further rotation, the light output will be restore