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. The principle that light travels such that the optical path length (or time) is equal along all rays explains this, as the slower speed in a denser medium balances the shorter path. Using Δ = d sinθ, y = n λ D/d, a sinθ = n λ,