Question

(i) State Malus's Law.
(ii) Draw a graph showing the variation of intensity (I) of polarised light transmitted by an analyser with angle $\left(\theta \right)$ between polariser and analyser.
(iii) What is the value of refractive index of a medium of polarising angle ${60}^{\circ }$ ?

Answer 1

(i) Malus discovered that when a beam of completely plane polarized light is passed through the analyser, the intensity 'I' of transmitted light changes directly as the square of the cosine of the angle $\left(\theta \right)$ between the transmission directions of polarizer and analyzer. This is known as the law of Malus.

$I\propto co{s}^2\theta$

or $I=I_{0}co{s}^2\theta$

Where,$I_0$ is the maximum intensity of the transmitted light.

(ii)
(iii) From the Brewster's law of polarization :

$\mu =tan{i}_p$

$=tan{60}^{\circ }$

$=\sqrt{3}$

$=1.7320$
Thus, the refractive index of the material is 1.73