Question

An unpolarised beam of light of intensity $I_0$ passes through two linear polarisers making an angle of $30^{\circ }$ with respect to each other. The emergent beam will have an intensity

• A. $\frac{3I_0}{4}$
• B. $\frac{\sqrt{3}{I}_0}{4}$
• C. $\frac{3I_0}{8}$
• D. $\frac{I_0}{8}$

Answer 1

Answer: (C)

Intensity after first polaroid $=\frac{I_0}{2}$
and intensity after second polaroid from Malus’ law is
$I=\frac{I_0}{2}\times {\cos }^2\theta$
$=\frac{I_0}{2}\times {\cos }^{2}30^{\circ }$
$=\frac{I_0}{2}\times \frac{3}{4}=\frac{3}{8}{I}_0$