Question

Polarized light passes through a polarizer, and only 20% gets through. find the angle between the light's electric field and the polarizer's transmission axis

Answer 1

according to Malus's law,
       I = I₀cos²Θ
here,  I is the intensity of light that gets through,
         I₀ is the intensity incident on polarizer  and Θ is the angle between light's electric field and the polarzer's transmission axis.
 
here, I = 20% of I₀ = 0.2I₀
so, 0.2I₀ = I₀cos²Θ
⇒ 0.2 = cos²Θ
⇒ Θ = cos⁻¹(√0.2)

Answer 2

As Light is Polarized, we use Malus Law:
I=I₀Cos²θ
where θ is the  angle between the light's electric field and the polarizer's transmission axis.
I=Intensity of light that passes through.
I₀=Intensity of light that is incident on polarizer.

According to given :only 20% gets through.
I=20%I₀
I=[20/100 ]xI₀
I=0.2I₀

0.2I₀=I₀ Cos²θ

0.2=Cos²θ

θ=Cos⁻¹(√0.2)