Practice question

**Classical wave theory fails** to explain instant emission, threshold existence, K_max dependence on frequency not intensity, saturation current dependence on intensity. Observations: K_max independent of intensity, exists threshold frequency, emission instantaneous, all explained by photon model E = h f, one photon ejects one electron, energy conservation h f = Φ + K_max. Φ₀ = h v₀ = 6.63 × 10⁻³⁴ × 3.0 × 10¹⁴ = 1.989 × 10⁻¹⁹ J . E = (h c/λ) = (6.63 × 10⁻³⁴ × 3 × 10⁸/500 × 10⁻⁹) = 3.978 × 10⁻¹⁹ J . Kₘₐₓ = E - Φ₀ = 3.978 × 10⁻¹⁹ - 1.989 × 10⁻¹⁹ =