Photoelectric Effect Calculator (Work Function)

How it works

KE_max = h·f − φ = h·c ÷ λ − φ · Stopping voltage V₀ = KE_max ÷ e · Threshold λ₀ = h·c ÷ φ

Einstein’s photoelectric equation says each photon delivers energy h·f = h·c/λ, and an electron escapes only if that exceeds the metal’s work function φ. Whatever energy is left over becomes the electron’s maximum kinetic energy, KE_max = h·f − φ. Crucially the energy depends on the light’s frequency, not its brightness: below the threshold frequency no electrons come out no matter how intense the light — the observation that forced physics to accept the photon.

Worked example

400 nm light on sodium (φ = 2.3 eV): photon energy = hc/λ = (6.626×10⁻³⁴ × 3×10⁸)/(400×10⁻⁹) ≈ 4.97×10⁻¹⁹ J ≈ 3.10 eV. KE_max = 3.10 − 2.3 = 0.80 eV, so a stopping voltage of about 0.80 V halts the fastest electrons. The threshold wavelength is hc/φ ≈ 539 nm.

Sources: Photoelectric effect — Wikipedia

Frequently asked questions