Unpolarized light of intensity I₀ = 100 W/m² passes through two Polaroid sheets. The first polarizer's axis is vertical; the second (analyzer) is at 30° to the vertical. (a) What is the intensity after the first polarizer? (b) After the second? (c) If the second is rotated to 90°, what happens? Solution: (a) An ideal polarizer transmits half of unpolarized light: I₁ = I₀/2 = 50 W/m², now vertically plane-polarized. (b) Malus's law: I₂ = I₁ cos²θ = 50 × cos²30° = 50 × 0.75 = 37.5 W/m². (c) At 90° (crossed polarizers), I₂ = 50 × cos²90° = 0 — no light passes (ideally). This is how LCD shutters block light.