Question

A beam of unpolarised light passes through a tourmaline crystal $A$ and then through another such crystal $B$ oriented so that the principal plane is parallel to $A$. The intensity of emergent light is $I$. If $A$ now rotated by ${45}^o$ in a plane perpendicular to direction of the incident ray. The emergent light will have intensity.

• A. $\frac{I}{2}$
• B. $\frac{I}{\sqrt{2}}$
• C. $I$
• D. $\frac{I}{4}$

Answer 1

Answer: (A)

$\frac{I}{2}$

According to law of Malus,
$I=I_{0}co{s}^2\theta =I_0(cos{45}^o{)}^2=I_0{\left(\frac{1}{\sqrt{2}}\right)}^2=\frac{I_0}{2}$