Practice question

**Intensity not depend on speed** when enters denser medium because intensity I ∝ n E₀²? Actually Poynting vector S = E×H, energy density u =½ ε E², for same amplitude E₀ intensity proportional to n, but amplitude changes at interface due to reflection, total energy conserved incident = reflected + transmitted, interference does not destroy energy, it redistributes. Bright fringe position x_n = (n λ D/d) . Fringes coincide when n₁ λ₁ = n₂ λ₂ . 600 n₁ = 400 n₂ , n₂ = (3/2) n₁ . Smallest integers: n₁ = 2 , n₂ = 3 . x = (2 × 6.0 × 10⁻⁷ ×