The photoelectric effect — light knocking electrons out of a metal surface — looks simple in the lab but broke classical physics when it was first studied carefully. Einstein's 1905 explanation, that light delivers its energy in discrete photon packets rather than as a continuous wave, became one of the founding results of quantum mechanics.
How the Photoelectric Effect Calculator works
The calculator applies Einstein's photoelectric equation, KEmax = hf − φ, where h is Planck's constant, f is the incident light's frequency, and φ is the target material's work function. You can enter the light either as a frequency (THz) or a wavelength (nm) — internally the calculator converts wavelength to frequency via c = fλ before applying the formula, since energy depends on frequency, not wavelength directly. From KEmax it also derives the threshold frequency f₀ = φ/h (the point where KEmax hits zero) and the stopping voltage V₀ = KEmax/e (the retarding potential that halts the fastest photoelectrons). All three quantities come from the same two inputs — the tabs simply choose which one is promoted to the headline result.
Inputs and what they mean
Frequency is entered in terahertz (10¹² Hz) since visible-to-UV light sits in the hundreds-of-THz range; wavelength is entered in nanometres for the same reason. The work function is entered directly in electronvolts, since that is how it is universally tabulated for real materials — typical metals range from about 2 eV (alkali metals like sodium, cesium) up to nearly 6.5 eV for platinum. The threshold frequency and stopping voltage depend only on the work function (and, for stopping voltage, on the light's frequency too) — they are properties of the material and the chosen light source, not adjustable independently.
Limits and edge cases
When the incident photon energy is below the work function, KEmax is mathematically negative — physically this means zero photoelectrons are emitted, not a beam of negative-energy electrons, so the calculator reports "No emission" rather than a negative kinetic energy on the headline result. This calculator assumes an ideal, clean metal surface and normal-incidence monochromatic light; real photoemission experiments see surface contamination, work-function variation across crystal facets, and a spread of electron energies below KEmax due to electrons escaping from below the very top atomic layer. It also does not model photon flux, quantum efficiency, or the photoelectric current itself — only the energetics of the fastest ejected electron.