1. The problem statement, all variables and given/known data This is problem 71, chapter 38 in Physics for Scientists and Engineers 8th edition by Serway/Jewett. Three polarizers are situated in a straight line with one spinning in the middle with θ=ωt. Find the intensity of light coming out the other side as a function of time. The attachment is the diagram of the system. 2. Relevant equations Manus's Law: I = Imax cos2 θ. Where θ is the angle between the transmission axis for the two polarizers. 3. The attempt at a solution Through the first two polarizers we have: I= Imax cos2 θ = Imax cos2 ωt which becomes I= Imax/2 (1+ cos(2ωt)) Then the light from the second polarizer is: I= Imax/2 (1+ cos(2ωt)) cos2 (90-ωt)= Imax/2 (1+ cos(2ωt)) sin2 (ωt) and this turns into: Imax/4 (1+ cos(2ωt))(1- cos(2ωt)) Imax/4 (1- cos2 (2ωt)) Imax/4 (1-(1+cos(4ωt)/2)) And for the answer we have: Imax/8 (1- cos(4ωt)) The problem is the book expects the solution to be: Imax/16 (1- cos(4ωt)) So I am off by a factor of 2. Can anyone see my problem or could it be a typo?