Question

Show that if you have three polarizing filters, with the second at an angle of 45 degrees to the first and the third at an angle of 90 degrees to the first, the intensity of light passed by the first will be reduced to 25% of its value. (This is in contrast to having only the first and third, which reduces the intensity to zero, so that placing the second between them increases the intensity of the transmitted light.)

Answer 1

I₃ /I₀ = 25%

Step-by-step explanation:

For this exercise let's use Malus's law

I = I₀ cos² θ

where tea is the angle between the two polarizers.

When the polarized light passes the first polarizer, the intensity is constant if it is in the direction of polarization.

I₁ = I₀

the light transmitted by the second polarizer is

I₂ = I₁ cos² θ

I₂ = I₀ cos² 45

I₂ = I₀ 0.5

this light is polarized 45º with respect to the first polarizer

Now let's examine the third polarizer, it is indicated that it has an angle of 90º with respect to the first polarizer, the angle with respect to the second polarizer is

θ = 90 - 45

θ = 45º

so the polarizer is at an angle of 45º

let's use Maus's law

I₃ = I₂ cos² 45

I₃ = I₀ 0.5 cos² 45

I₃ = I₀ 0.25

the light that passes through the system is

I₃ /I₀ = 0.25

as a percentage we multiply by 100

I₃ /I₀ = 25%