Explanation

(a) According to law of Malus, when a beam of completely plane polarized 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 polarizer
$ie,\ I \propto \cos^{2}\theta$ and $I = I_{0}\cos^{2}\theta$ …(i)
[image:10_image46.emf]
Where $I_{0} =$ intensity of the light from polarizer
From Eq. (i), we note that if the transmission axes of polarizer 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 polarizer and analyser are perpendicular $(ie,\ \theta = 90{^\circ})$, 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