Question

An unpolarized light beam of 800 W/m2 is incident on an ideal pair of crossed linear polarizers. Crossed polarizers indicate that the transmission axes of the polarizers are at 900 to one another. Now, a third polarizer is inserted between the other two with its transmission axis at 450 to that of each of the others. Determine the emerging intensity

a) before and

b) after the insertion of the third polarizer c) explain the results of parts a) and b).

Answer 1

(a) when they are at 900 to each other, emerging intensity I = 800*(cos90)^2 = 0

(b) a third polarizer is inserted between the other two with its transmission axis at 450 to that of each of the others, then emerging intensity I = 800*(cos45)^2*(cos45)^2 = 200W/m2

(c) In a all Intensity is zero because of crossed linear polarizers as their transmission axes are at 900 to one another, and the component in this direction is 0. But in b, they are at 450 to that of each of the others so that some part is always passed and Intensity is only reduced.