Malus Law
By Un-polarized light gets linearly polarized when it passes through a polarizer. When, a linearly polarized light passes through another polarizer (called analyzer), the intensity of transmitted light depends on the angle $\theta$ between polarization axis and analyzer axis. The intensity of the transmitted light is given by Malus's law \begin{align} I=I_0\cos^2\theta, \end{align} where $I_0$ is the intensity of the incoming light and $\theta$ is the angle between the polarizer and the plane of polarization of the incoming light.
