Q 12-10-002NEETNEET 2025Top questionMedium
The intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at $22.5°$ from the polarization axis of one of the polaroid, is ($I_0$ is the intensity of polarised light after passing through the first polaroid):
Answer: (C) $\dfrac{I_0}{8}$
Concept. Malus's law at each sheet: $I = I_0\cos^2\theta$.
Step 1. Angles. The middle sheet is at $22.5°$ to the first and $67.5°$ to the crossed second.
Step 2. Intensity.
$$I = I_0\cos^222.5°\cos^267.5° = I_0(\cos22.5°\sin22.5°)^2 = I_0\left(\frac{\sin45°}{2}\right)^2 = \frac{I_0}{8}$$
Answer. $\dfrac{I_0}{8}$ (Option C).
Solution by Sreeraj P, M.Sc Physics