Question

The irradiance of a beam of natural light is 400 W/m². It impinges on the first of two consecutive ideal linear polarizers whose transmission axes are 40.0° apart. How much light emerges from the two?

Answer 1

$I=I_0\cos^2\alpha,$

$I=400\cdot \cos^2 40°=235~\frac{W}{m^2}.$