Find the maximum kinetic energy of electrons ejected by light with KEₘₐₓ = h·f − φ — enter the light's frequency and the metal's work function (eV or joules). Also shows the threshold frequency.
In the photoelectric effect, light striking a metal ejects electrons only if each photon carries enough energy. A photon's energy is hf; the metal holds electrons with a binding energy called the work function φ. The leftover appears as kinetic energy: KEₘₐₓ = hf − φ.
If hf is below φ, no electrons escape no matter how bright the light — this threshold behaviour was Einstein's evidence for photons. The threshold frequency is f₀ = φ/h. Enter the work function in eV or joules using the unit selector.
For the underlying physics, read our explanation of light quanta and the photoelectric effect.
The maximum kinetic energy of ejected electrons is KEmax = hf − φ, where h is Planck's constant, f the light frequency and φ the metal's work function.
The work function φ is the minimum energy needed to remove an electron from a metal's surface, typically a few electronvolts. Different metals have different values.
The threshold frequency f₀ = φ/h is the lowest light frequency that can eject electrons. Below it, no electrons are emitted regardless of intensity.
Because emission depends on frequency, not brightness — only photons above the threshold energy free electrons. This showed light delivers energy in discrete quanta, which won Einstein the Nobel Prize.