Question

In a system of two crossed polarisers, it is found that the intensity of light from the second polariser is half from that of first polariser. The angle between their pass axes is

• A. $45^{\circ }$
• B. $60^{\circ }$
• C. $30^{\circ }$
• D. $0^{\circ }$

Answer 1

Answer: (A)

Let the angle between two polarizers be $\theta$ and maximum intensity of the light be $I_0$.
From Malus law, Intensity of light after passing through the polarizers $I=I_0{\cos }^2\theta$
Given : $I=\frac{I_0}{2}$
$\therefore \frac{I_o}{2}=I_o{\cos }^2\theta$
Or ${\cos }^2\theta =\frac{1}{2}$
Or $\cos \theta =\frac{1}{\sqrt{2}}$
$⟹\theta =45^{\circ }\text{. }$