Question

What happens when two polarizers are placed in a straight line, one behind the other?

Answer 1

When two polarizers are placed in a straight line, they allow light to pass only if their directions of polarizations are exactly 90° apart.   

To add, a polarizer or polariser is an optical filter that lets light waves of a specific polarization pass and blocks light waves of other polarizations.

Answer 2

Answer: The intensity of the light would depend upon the angle between the two polarizers.

Explanation:

When two polarizers are placed in a straight line, one behind the other, the intensity of the light coming from the analyser would be directly proportional to the square of the cosine angle of the polarizer according to Law of Malus.

Amplitude of the light varies as:

A = A₀ cosθ

Intensity of the light:

I ∝ A²

⇒ I ∝ cos²θ

At θ =0°

Intensity of light exiting analyser would be same as the light entering polarizer, because cos 0° = 1

At θ = 90°

Intensity of light exiting analyser would be zero because cos 90° = 0