Question

The graph showing the dependence of intensity $(I)$ of transmitted light on the angle $(\theta )$ between polariser and analyser, is

• A.
• B.
• C.
• D.

Answer 1

Answer: (B)

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.
i.e., $I\propto {\cos }^2\theta$
and $I=I_0{\cos }^2\theta .......$(i)

where $I_0=$ intensity of the light from polariser.
From equation (i), we note that if the transmission axes of polariserand analyserare parallel(i.e., $\theta =0^{\circ }$ 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 (i.e., $\theta =90^{\circ }$ ), then $I=I{\cos }^{2}90^{\circ }=0$. 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.