Question

Unpolarised light is incident on a polaroid. How would the intensity of transmitted light change when the polaroid is rotated?

Answer 1

If the unpolarised light is incident on a Polaroid the intensity is reduced by half. Even if the Polaroid is rotated by angle θ the average over cos²θ = ½. Thus from Malus’ law: I = I₀cos²θ

Or, = < I₀cos²θ > = I₀< cos²θ > = I₀/2

Thus, the intensity of the transmitted light remains unchanged when the Polaroid is rotated.