Photons and the photoelectric effect · Year 13
Light comes in packets of energy called photons, each with energy E = hf. This explains the photoelectric effect: light only frees electrons from a metal if each photon has more energy than the work function, no matter how bright the light. Moving particles like electrons also behave as waves. These ideas founded quantum physics and power solar cells and electron microscopes.
Key facts
- Photon energy E = hf = hc ÷ λ, with h = 6.63 × 10⁻³⁴ J s and c = 3.0 × 10⁸ m/s.
- 1 eV = 1.6 × 10⁻¹⁹ J.
- Photoelectric equation: hf = φ + E_k(max); threshold frequency f₀ = φ ÷ h.
- Brighter light (same frequency) frees more electrons, but not faster ones.
- Stopping potential: eV_s = E_k(max).
- de Broglie wavelength λ = h ÷ (mv); electron diffraction shows particles behave as waves.