Question

A beam of polarized light is incident on a system of three polarizers. The incident lig is polarized at an angle of 30° with respect to the first polarizer. The second polarizer is oriented at an angle of 40 ° with respect to the first, and the third is oriented at an angle of 35 with respect to the second. If the light that emerges from the system has an intensity of 2.5 W/m2, what is the intensity of the incident light, in W/m2?

Answer 1

You need to know two relations for this problem. Malus Law, $I = I_0 \cos^2(\theta).$ $I_0$ is the initial incident intensity, $\theta$ is the angle the incident polarized light's polarization angle makes with the polarizer. And that the initial (first) polarizer halfs the intensity irrespective of the incident angle. Knowing these two basic facts we can go about computing the unknown in this above problem.

Call the initial incident light intensity

10.

So,

Io → Io cos? (7/6) 0.29532410 310 o cos?(40°) = 0.44011819 +0.440118/o cos? (35°)

Now, $0.295324 I_0 = 2.5 \implies I_0 = 8.46529 ~ W/m^2.$