What is the intensity of light after passing through two polaroids with their pass-axes perpendicular to each other, if
**Polaroid rotation** intensity varies sinusoidally with angle due to Malus law I = I₀ cos²θ, when polaroid rotated 90° from initial, intensity goes from max to zero, for unpolarized light rotating polaroid does not change intensity after first polaroid because average, but second polaroid intensity depends on relative angle, explains why intensity transmitted through two polaroids drops to zero when perpendicular. After the first polaroid, intensity is (I₀/2) . For the second polaroid at 90° , I = (I₀/2) cos² 90° = (I₀/2) × 0 = 0 . Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ, I =
Ref: NCERT > Physics Book > Wave Optics > Polarization and Malus Law