Photoelectric Effect Simulator (2D)

Metal Target

Light Source

Frequency f 6.00 ×10¹⁴ Hz

Wavelength λ 500 nm

Intensity (brightness) 60%

Below threshold — no electrons ejected.

Live Readout

Photon energy hf

2.48 eV

Work function φ

2.10 eV

Threshold f₀

5.08 ×10¹⁴ Hz

Electrons / s

Max kinetic energy KE_max = hf − φ

0.00 eV

Stopping voltage

0.00 V

How it works

Classical wave theory predicted that a brighter light beam should always eject electrons eventually, given enough time to build up energy, and that electron energy should rise with brightness. Real metal plates flatly refused to behave that way — which is what Einstein explained in 1905 by treating light as a stream of discrete photons, each carrying energy E = hf (h = Planck's constant, f = frequency).

A single photon can free a single electron only if its energy exceeds the metal's work function φ — the minimum energy binding an electron to the surface. Below the threshold frequency f₀ = φ/h, every photon is too weak individually, so turning up the intensity just delivers more too-weak photons per second: still zero electrons, no matter how bright the light.

Above threshold, each absorbed photon ejects one electron instantly, with maximum kinetic energy KE_max = hf − φ — set entirely by frequency, never by intensity.
Raising intensity above threshold increases the number of photons arriving per second, so more electrons are ejected per second, but each one still leaves with the same KE_max.
The stopping voltage is the retarding potential that just barely halts the fastest ejected electron; numerically it equals KE_max expressed in electron-volts.