According to law of Malus, when a beam of completely plane polarised light is incident on an analyser, the resultant intensity of light (I) transmitted from the analyser varies directly as the square of the cosine of the angle $(\theta)$ between planes of transmission of analyser and polariser.
ie, $I \propto \cos ^{2} \theta$
and $I=I_{0} \cos ^{2} \theta$ ... (i)
where $I_{0}=$ intensity of the light from polariser.
From Eq. (i), we note that if the transmission axes of polariser and analyser are parallel (ie, $\theta=0^{\circ}$ or $180^{\circ}$, then $I=I_{0}$. It means that intensity of transmitted light is maximum. When the transmission axes of polariser and analyser are perpendicular $\left(i e, \theta=90^{\circ}\right)$, then $I=I_{0} \cos ^{2} 90^{\circ}=0$. It means the intensity of transmitted light is minimum.
On plotting a graph between $I$ and $\theta$ as given by relation (i), we get the curve as shown in figure.
