Question

Two polarizers are placed at crossed position and the angle between the polarizing planes is 90°. A third polarizer with angle ߠ with the first one is placed between them. An unpolarized light of intensity ܫ ଴is incident on the first one and passes through all three polarizers. Find the intensity of the light that comes out. Now if the third polarizer is made to rotate with angular frequency
w about the incident ray as axis show that the emergent intensity will be I/16cos^-1(1 − cos 4wt)

Answer 1

Answer:

If incident intensity is Io on first polariser, intensity of light transmitted by first polariser is ( Io /2 ) .

 If polariser P2 makes an pass angle θ with P1 , then by Malus law, transmitted intensity by P2 = ( Io /2 ) Cos2θ

 Since P1 and P3 are having pass angles perpendicular to each other, pass angle of P3 with respect to P2 = 90 - θ

 Hence transmitted intensity by P3 = ( Io /2 ) Cos2θ Cos2(90-θ) = ( Io /2 ) Cos2θ Sin2θ