Malus's Law governs intensity through polarizers

Steps:

• Initial vertical polarization at 45° to first filter's axis yields I₁ = I₀ cos²(45°) = I₀ (1/√2)² = ½ I₀, polarized at 45°.
• Light now at 45° to second filter's horizontal axis (90° from vertical), so angle φ = 45°.
• Intensity after second filter: I₂ = I₁ cos²(45°) = ½ I₀ × ½ = ¼ I₀.
• Result follows sequential application of Malus's law.

Why B is correct:

• Malus's law states transmitted intensity is I = I_in cos²θ, where θ is angle between polarization and transmission axis; here, two 45° angles each reduce by ½.

Why the others are wrong:

• A: Ignores partial transmission at 45° angles; zero only if θ=90°.
• C: Matches first filter only, neglects second filter's 45° reduction.
• D: Assumes no polarization loss, but filters absorb based on angle.

Final answer: B