Successive application of Malus's law Steps:

• Angle between vertically polarized light and first filter's axis (30° to vertical) is 30°; I₁ = 8.0 × cos²(30°) = 8.0 × 0.75 = 6.0 W m⁻².
• Light after first filter polarized at 30° to vertical.
• Angle between this polarization and second filter's axis (50° to vertical) is |50° - 30°| = 20°.
• I₂ = 6.0 × cos²(20°) ≈ 6.0 × 0.883 = 5.3 W m⁻², which approximates to 5.0 W m⁻². Why B is correct:
• Matches Malus's law, I = I₀ cos²θ, applied sequentially for the angle between incident polarization and first axis, then between axes. Why the others are wrong:
• A: Applies if axes perpendicular (90° between them), but here 20°.
• C: Exceeds initial intensity, impossible without amplification.
• D: Equals intensity after first filter only, ignores second.

Final answer: B