Question

Unpolarised light rays of intensity ${\text{I}}_0$ is passed through a polaroid $\text{A}$ and then through another polaroid $\text{B}$ which is oriented in such a way that its principal plane makes an angle of ${\text{45}}^{\text{o}}$ relative to that of $\text{A}$ . What will be the intensity of the emergent light?

• A. $\frac{{\text{I}}_0}{4}$
• B. $\frac{{\text{I}}_0}{8}$
• C. ${\text{I}}_0$
• D. $\frac{{\text{I}}_0}{2}$

Answer 1

Answer: (A)

Relation between intensities is

When unpolarised light passes the polaroid, intensity become half.
$I_A=\frac{I_o}{2}$
${\left(\text{I}\right)}_B=I_A{\left(\text{ cos}\right)}^2\left({\left(\text{45}\right)}^{\text{o}}\right){\left(\text{I}\right)}_B=\left(\frac{{\left(\text{I}\right)}_0}{2}\right){\left(\text{ cos}\right)}^2\left({\left(\text{45}\right)}^{\text{o}}\right)=\frac{{\left(\text{I}\right)}_0}{2}\times \frac{1}{2}=\frac{{\left(\text{I}\right)}_0}{4}$