How Does Malus's Law Apply to Light Intensity with Three Polarizers?

[ronaldoshaky]

Hello I am trying to understand Malus' Law and the Intensity of light. Let's say I have three polarizers. The first polarizer and the last polarizer have the same axis of polarization. The middle polarizer can be rotated to an angle \theta

I know that Malus's Law for the intensity of light is I = I_0 cos^2 \theta for light coming out through the second polarizer. But how would I work out the intensity of light passing through the third filter. Should I multiply by cos^2 \theta again, or should I treat the final two polarizers as just two polarizers?

 

[Doc Al]

Treat each polarizer in the same manner, applying Malus's law as needed. After the light exits the second polarizer, what is its axis of polarization? What's the angle between the second and third polarizers? That's the angle you'll need in applying Malus's law to the light passing that third polarizer.

 

[ronaldoshaky]

Treat each polarizer in the same manner, applying Malus's law as needed. After the light exits the second polarizer, what is its axis of polarization? What's the angle between the second and third polarizers? That's the angle you'll need in applying Malus's law to the light passing that third polarizer.

Ah I see. Thanks