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
$I=\frac{I_{0}}{2}\times \cos^{2}\theta$
$=\frac{I_{0}}{2}\times \cos^{2}30^{\circ}$
$=\frac{I_{0}}{2}\times\frac{3}{4}=\frac{3}{8}I_{0}$