The Photoelectric Effect
Light can eject electrons from a metal surface only when each photon carries enough energy. This supports the quantum photon model of light.
Threshold frequency
Below a metal-specific cutoff frequency, no electrons are emitted regardless of intensity. Each photon must exceed the work function energy.
Kinetic energy of photoelectrons
Einstein's equation Kmax = hf − φ links photon frequency to maximum electron kinetic energy. Increasing intensity adds more photons, not higher energy per photon.
Simulate the effect
Use the photoelectric simulation to vary wavelength, observe electron emission, and find the stopping potential for different metals.
Light doesn't hit a metal as a smooth wave — it arrives in tiny bursts called photons, each carrying a fixed amount of energy. An electron escapes only if a single photon's energy is at least as big as the metal's work function, the energy that normally holds the electron in place. Whatever energy is left over becomes the kinetic energy of the electron as it flies off.
KEₘₐₓ = h · f − φ
- KEₘₐₓ — maximum kinetic energy (eV): the greatest energy an ejected electron carries away
- h — Planck's constant (eV·s): tiny constant linking a photon's frequency to its energy
- f — frequency (Hz): how many light waves arrive each second
- φ — work function (eV): minimum energy needed to pull an electron free from the metal
A photon striking a sodium surface carries 3.1 eV of energy. Sodium's work function is 2.1 eV. What is the maximum kinetic energy of an ejected electron?
- hf = 3.1 eV
- φ = 2.1 eV
- KEₘₐₓ = h · f − φ
- KEₘₐₓ = 3.1 eV − 2.1 eV
KEₘₐₓ = 1.0 eV