Question

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

• A. $10\%$
• B. $20\%$
• C. $25\%$
• D. $12.5\%$

Answer 1

Answer: (D)

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