Question

Two polaroids are kept crossed to each other. If one of them is rotated an angle ${60}^o$, the percentage of incident light now transmitted through the system is

• A. 10%
• B. 20%
• C. 25%
• D. 12.5%

Answer 1

Answer: (D)

12.5%

Let the intensity of unpolarized light be $I_0$, so the intensity of the first polaroid is $\frac{I_0}{2}$.
On rotating through ${60}^o$, the intensity of light from second polaroid
$I=\left(\frac{I_0}{2}\right)(cos60{)}^2=\frac{I_0}{2}\frac{1}{4}=\frac{I_0}{8}=0.125I_0$
$\therefore$ percentage of incident light transmitted through the system = $12.5$%