Consider two polaroids A and B as shown. Unpolarised light is incident on polaroid A . Now, both the polaroids are rotated simultaneously by 180 ° in the same sense of rotation such that at every instant, their pass (transmission) axes always remain parallel to each other. During the rotation, intensity of transmitted light through polaroid B

Step-by-step solution

Intensity after passing through polaroid A is I A = I 0 2 = I n t e n s i t y o f u p o l a r i s e d l i g h t 2 Intensity after passing through polaroid B is I B = I A cos 2 ⁡ θ Here, θ = angle between pass axes of A and B . Here, pass (transmission) axes always remain parallel to each other i.e. θ = 0 . ∴ I B = I A = I 0 2 = c o n s t a n t Hence, during the rotation, the intensity of transmitted light through polaroid B remains the same.