Question

A system of three polarizers $P_1,P_2,P_3$ is set up such that the pass axis of $P_3$ is crossed with respect to that of $P_1$. The pass axis of $P_2$ is inclined at 60º to the pass axis of $P_3$. When a beam of unpolarized light of intensity $I_0$ is incident on $p_1$, the intensity of light transmitted by the three polarizers is $I$. The ratio $(I_0/I)$ equals (nearly) :

• A. 16.00
• B. 1.80
• C. 5.33
• D. 10.67

Answer 1

Answer: (D)

Since unpolarised light falls on $P_1\Rightarrow$ intensity
of light transmitted from $P_1=\frac{I_0}{2}$
Pass axis of $P_2$ will be at an angle of $30^{\circ }$ with
$P_1$
$\therefore$ Intensity of light transmitted from
$P_2=\frac{I_0}{2}co{s}^{2}30^{\circ }=\frac{3I_0}{8}$
Pass axis of $P_3$ is at an angle of $60^{\circ }$ with $P_2$
$\therefore$ Intensity of light transmitted from
$P_3\frac{3I_0}{8}co{s}^{2}60^{\circ }=\frac{3I_0}{32}$
$\therefore \left(\frac{I_0}{I}\right)=\frac{32}{3}=10.67$