The Photoelectric Effect

Light ejects electrons from a metal only when each photon carries more energy than the work function: Kmax = hc/λ − φ. Brighter light means more electrons, never faster ones — energy comes from the wavelength, not the intensity.

Max kinetic energy  Kmax = E − φ
0.80 eV
electrons emitted
Photon energy E
3.10 eV
Stopping V0
0.80 V
Wavelength λ400 nm
Intensity60%
Work function φ2.30 eV
Threshold λ0539 nm
Relative current60%
Emissionon
h = 6.62607015 × 10-34 J·s · c = 2.998 × 108 m/s · e = 1.602 × 10-19 C
Tip: raise λ past the threshold λ0 and emission stops dead — no matter how bright the light.