Intensity of unpolarized light through two polarizers

[Linus Pauling]

1. Unpolarized light with intensity 440 W/m² passes first through a polarizing filter with its axis vertical, then through a polarizing filter with its axis 20.0 degrees from vertical.



2. Malus's Law



3. Ok, the intensity after going through the first polarizer should be 1/2 the original. This, after the second polarizer, I = 220*cos20) = 207 W/m², which is incorrect.

 

[vela]

The filter works by allowing only the parallel component of the electric field, E cos(theta), through. How are the electric field of the light and the intensity of the light related?

 

[Linus Pauling]

I = P/A = 0.5c*epsilon_0*E^2

Again, I don't see how to get I from P without knowing A.

 

[vela]

You're getting too caught up in just brute force calculation when you should be focusing on how one quantity depends on another. You don't need to know P or A. Think ratios.