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.
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.