Practice question

**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, I = (I₀/2) . After the second at 30° , I = (I₀/2) cos² 30° = (I₀/2) × (3/4) = (3I₀/8) . Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ, I = I₀