To solve the problem it is necessary to apply the Malus Law. Malus's law indicates that the intensity of a linearly polarized beam of light, which passes through a perfect analyzer with a vertical optical axis is equivalent to:
[tex]I=I_0 cos^2\theta[/tex]
Where,
[tex]I_ {0}[/tex] indicates the intensity of the light before passing through the polarizer,
I is the resulting intensity, and
[tex]\theta[/tex] indicates the angle between the axis of the analyzer and the polarization axis of the incident light.
Since we have two objects the law would be,
[tex]I=I_0cos^2\theta_1*cos^2(\theta_2-\theta_1)[/tex]
Replacing the values,
[tex]I=100*cos^2(20)*cos^2(40-20)[/tex]
[tex]I=100*cos^4(20)[/tex]
[tex]I=77.91W/m^2[/tex]
Therefore the intesity of the light after it has passes through both polarizers is [tex]77.91W/m^2[/tex]
