Practice question

**Photon power** light source emits 1.0×10¹⁶ photons/s power 4.0 mW, energy per photon E= P/N =4×10⁻³/10¹⁶=4×10⁻¹⁹ J, wavelength λ= h c/E=6.63×10⁻³⁴×3×10⁸/4×10⁻¹⁹=497 nm, for 6×10¹⁵ photons/s 3.0 mW E=5×10⁻¹⁹ J, for beam 2.5×10¹⁵ photons/s 4×10⁻¹⁹ J each power=10⁻³ W=1 mW, illustrating P = N h f. Photon momentum p = (h/λ) = (6.63 × 10⁻³⁴/500 × 10⁻⁹) = 1.326 × 10⁻²⁷ kg m/s . v = (p/m) = (1.326 × 10⁻²⁷/1.5 × 10⁻³⁰) = 8.84 × 10² = 884 m/s . Applying E = h f = h c/λ, p = h/λ, K_max = h f - Φ, Φ = h f₀ = h c/λ₀, λ