Photoelectric effect
Explore photon energy, stopping voltage and photocurrent with explicit optical power and efficiency.
About this tool
All valid changes update immediately, including the initial view. Material examples set the work function; Custom opens Options for an exact work function and the assumed quantum efficiency η. The default 10% is illustrative, not a measured property of the material. Work functions depend on surface conditions in real experiments. Exact wavelength and voltage fields have live sliders; clicking inside the I–V plot sets the voltage. Positive anode voltage attracts electrons; negative voltage retards them. Reset restores all defaults and clears the model points.
Photon energy is hf = hc/λ. If hf exceeds φ, the maximum electron kinetic energy is hf − φ and the stopping voltage is V₀ = (hf − φ)/e. Below threshold there is no photoemission regardless of optical power. At exactly the threshold the ideal outgoing kinetic energy is zero; this model uses no finite current. Unavailable kinetic energy and stopping voltage are shown as dashes. Changing power or η does not change V₀.
For optical power P in watts and a constant assumed emitted-electron yield η, I_sat = η e P/(hf). Increasing power at fixed wavelength changes current linearly; at fixed power a longer wavelength supplies more photons. Actual yield varies with wavelength and material. The illustrative I–V law assumes uniformly distributed effective normal escape energies: I = 0 for V ≤ −V₀, I = I_sat(1 + V/V₀) for −V₀ < V < 0, and I = I_sat for V ≥ 0. It is not a calibrated real-tube characteristic and includes no dark current, contact potential, angular distribution or multiphoton effects.
In Einstein line, add calculated points at different above-threshold wavelengths. Duplicates are disabled. Work-function or material edits clear the series; changing power, voltage or efficiency keeps it. At most 24 points are retained. A centered linear fit requires separated frequencies and shows h in J·s and the intercept-derived work function. These noiseless model points are generated from the known h, so the fit is a consistency demonstration, not a measurement of Planck’s constant.
The optional eight-second schematic uses uniform-field trajectories, with each flight time rescaled for visibility. Electrons lacking enough energy return to the cathode; emission can continue even when the collector current is zero. Colors, counts and timing illustrate behavior and are not detector counts or real flight times. Pause, edits, view changes and hidden pages stop playback. Reduced motion disables playback. Valid settings persist across navigation; results and point series start fresh.
Only raw input texts, material and selected view are retained, including incomplete/invalid/comma values; valid legacy numeric settings migrate. Calculated currents, model points, fitted constants and playback positions are never saved. Reload reconstructs the chosen view with a fresh point series.