ONE PHOTON. ONE INTERACTION.
The photoelectric effect.
Change the energy of each photon, how many arrive, and the voltage that helps or opposes electron collection.
From photons to photocurrent
Incident photons Emitted electrons Current graph marker
Particles represent groups and are slowed for visibility. Higher intensity sends more photon groups each second. UV and infrared use symbolic colours. Adjust sliders live without restarting the photon stream. Readings and graphs show the steady-state prediction at your current settings.
Photocurrent against photon arrival rate
Photocurrent against voltage
Intensity changes the count. Frequency changes the energy.
Here h is Planck’s constant, f is photon frequency, φ is the metal’s work function and e is the elementary charge. Below the threshold frequency, brighter light still cannot release electrons in this single-photon model.
Turn up the intensity
At fixed frequency, more photons arrive each second. Above threshold, more electrons are emitted, so the photocurrent increases when electrons can reach the collector. The maximum kinetic energy and stopping potential stay the same.
Change the collector voltage
V = collector potential − emitter potential. Positive V accelerates electrons towards the collector. Negative V opposes them; a sufficiently negative voltage stops even the fastest photoelectrons. An accelerating voltage cannot release electrons when the light is below threshold.
How the current and animation are modelled
Finite collector in vacuum, with no contact potentials, space-charge effects or leakage current. Quantum efficiency is the percentage of photons that release an electron when photon energy exceeds the work function. The 10% button is an illustrative photocathode-style value, not a calibrated value for a particular bare metal or wavelength. The slider holds this chosen efficiency constant as you vary frequency; below threshold, emission is always zero.
Emitted electrons have a triangular energy distribution, with more low-energy electrons, and a cosine-weighted range of directions within ±60° of the surface normal. Light illuminates the central 40% of the emitter; the collector has finite height. Electrons that turn back or leave the collection region do not contribute to current. Positive voltage reduces sideways losses. The graphs numerically average this model, producing a curved rise and saturation at positive voltage. The curve is illustrative, not a fit to an experimental apparatus. At exactly threshold the model displays zero current.
Photon and electron groups are illustrative. Their travel is slowed; the current readings are steady-state calculations, not counts of animated dots. Photons already in flight retain their original energy and colour. Voltage changes affect the onward motion of existing electrons without resetting their positions; changes to work function and quantum efficiency apply to later photon impacts. The particle diagram is not to scale; the model uses an electrode gap-to-height ratio of 0.4. With a fixed illuminated area, the photon-rate control represents relative intensity; incident optical power is also shown.
Reference: OpenStax: Photoelectric Effect; Hamamatsu: photocathode quantum efficiency.
Explore the photoelectric effect
Control photon frequency, photon arrival rate, collector voltage and quantum efficiency. Watch continuous photon and electron motion while comparing photocurrent against photon arrival rate and voltage. Inspect threshold frequency, maximum emitted electron kinetic energy and stopping potential.
Supports photoelectric-effect study in IB Physics, A Level and AP Physics. The curved current–voltage characteristic models a distribution of emission energies and directions with a finite collector. Quantum efficiency is adjustable; the 10% preset is illustrative and is not a calibrated material response.