Three polarizing disks are arranged as shown. The left and right axes are perpendicular, while the middle disk rotates with angular speed ω. Unpolarized incident light has intensity Iₘₐₓ. Find the emerging intensity as a function of time.

Question

G1 Physics · Accepted Answer

Unpolarized light of intensity Iₘₐₓ becomes Iₘₐₓ/2 after the first polarizer. Let the rotating middle polarizer make θ=ωt with the first. After it, intensity is (Iₘₐₓ/2)cos²θ. The last polarizer is crossed with the first, so it contributes sin²θ. Hence I=(Iₘₐₓ/2)cos²θ sin²θ=(Iₘₐₓ/8)sin²2θ=(Iₘₐₓ/16)[1-cos4ωt]. Option A.