How can it be determined whether a given light is unpolarized,plane-polarized,or partially plane-polarized?

(N/A) To determine the state of polarization of a given light beam,place a polaroid in its path such that the light is incident perpendicularly on the polaroid surface.
Rotate the polaroid about the direction of the incident light beam as an axis and observe the intensity of the light emerging from the polaroid.
$1$. If the intensity of the emerging light remains constant throughout a full rotation of the polaroid,the light is unpolarized.
$2$. If the intensity of the emerging light varies such that it becomes zero twice and maximum twice during a full rotation,the light is plane-polarized.
$3$. If the intensity of the emerging light varies such that it becomes maximum twice and minimum (but not zero) twice during a full rotation,the light is partially plane-polarized.