Q. A beam of ordinary unpolarised light passes through a tourmaline crystal $C_{1}$ and then it passes through another tourmaline crystal $C_{2}$, which is oriented such that its principal plane is parallel to that of $C_{2}$. The intensity if emergent light is$I_{0}$. Now $C_{2}$ is rotated by $60{^\circ}$ about the ray. The emergent ray will have an intensity
A) $2I_{0}$
B) $I_{0}/2$
C) $I_{0}/4$
D) $I_{0}/\sqrt{2}$
Explanation
(c) Intensity of light from $C_{2} = I_{0}$
On rotating through $60{^\circ}$,
$I = I_{0}\cos^{2}{60{^\circ}}$ (law of Malus)
$= I_{0}\left( \frac{1}{2} \right)^{2} = I_{0}/4$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.