The Photoelectric Effect: Interactive demonstration showing how light frequency, not intensity, determines electron energy
Brighter Light Won't Make Electrons Faster
Einstein's 1905 explanation of the photoelectric effect revealed that light behaves as discrete photons, not continuous waves. Each photon transfers its energy to a single electron in a quantum interaction—and only frequency, not intensity, determines how much kinetic energy that electron gains. Drag the frequency slider to see how photon energy affects ejected electrons.
Photoelectric Emission
Below Threshold
Photon frequency controls electron energy
f < f₀ · No Emission
Low ff₀High f
Photon Energy
2.1 eV
Electron KE_max
0.0 eV
Increasing the frequency of incident light increases the energy of each individual photon (E = hf). When a photon strikes the metal surface, it transfers all its energy to a single electron in a quantum interaction. If the photon energy exceeds the work function φ, the electron is ejected with kinetic energy equal to the excess: KE_max = hf - φ. Higher frequency means more energetic photons, which directly increases the maximum kinetic energy of emitted electrons. This is why ultraviolet light ejects faster electrons than visible light, even if the UV beam is dimmer.
Know This
The photoelectric equation is hf = φ + KE_max, where φ is the work function and KE_max is the maximum kinetic energy of emitted electrons—only photons above the threshold frequency f₀ (defined by hf₀ = φ) can eject electrons, regardless of intensity.