# Intensity of unpolarized light through two polarizers

1. Apr 14, 2010

### 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.

2. Apr 14, 2010

### vela

Staff Emeritus
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?

3. Apr 14, 2010

### 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.

4. Apr 16, 2010

### vela

Staff Emeritus
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.