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Photoelectric Effect Calculator

Work out photoelectric effect instantly with clear inputs, formula shown and shareable results.

About Photoelectric Effect Calculator

Einstein's photoelectric equation is KE(max) = hf - phi. A 400 nm photon carries 3.10 eV, so on potassium (phi = 2.28 eV) the fastest electrons leave with 0.82 eV and are stopped by 0.82 V. Below the threshold wavelength nothing is emitted no matter how intense the light, which is what killed the classical wave picture.

Formulas

Photoelectric equation

KE(max) = h c / lambda - phi

Stopping voltage

V(stop) = KE(max) / e

Worked example

With the default values below, Photoelectric Effect Calculator returns Maximum Electron Kinetic Energy of 0.8196. Change any input above and every figure here is recalculated in your browser.

Inputs used

Wavelength of the incident lightminimum 0 nm
400 nm
Work function of the metalminimum 0 eV
2.28 eV

Results

Maximum Electron Kinetic Energy
0.8196 eV
Photon Energy
3.0996 eV
Stopping Voltage
0.8196 V
Maximum Electron Speed
5.3694 × 10⁵ m/s

Step by step

  1. 1Values used
  2. 2Photoelectric equation
  3. 3Stopping voltage
  4. 4Maximum Electron Kinetic Energy= 0.8196 eV
  5. 5Photon Energy= 3.0996 eV
  6. 6Stopping Voltage= 0.8196 V
  7. 7Maximum Electron Speed= 536,943.0000 m/s

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does brighter light not help below the threshold?

Because each electron absorbs one photon. More photons of insufficient energy still cannot free a single electron - the effect is per-photon, not cumulative.

What does the stopping voltage measure?

The potential needed to turn back even the fastest electrons, so it reads the maximum kinetic energy directly in electronvolts.

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