How this calculator works
A photon must supply the surface work function before the remaining energy can appear as photoelectron kinetic energy. Below threshold the output reports no emission and zero available kinetic energy. At threshold the ideal maximum kinetic energy is zero. Inverse work-function calculation assumes emission has occurred; a zero electron-energy observation alone cannot distinguish threshold from no emission. Stopping voltage is the magnitude needed to oppose the most energetic electrons. Surface contamination, temperature, multiphoton effects and contact potentials are outside the model.
Formula
Kmax = hf - phi = hc/lambda - phi when hf >= phi. Below threshold there is no photoemission. f0 = phi/h; lambda0 = hc/phi; stopping voltage magnitude = Kmax/e.
Worked example
An incident 5 eV photon on a surface with work function 2 eV produces maximum kinetic energy 3 eV and stopping voltage magnitude 3 V. A 1 eV photon cannot eject an electron from that surface.
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Frequently asked questions
Does brighter light increase maximum energy?
In the single-photon model intensity changes the number of emitted electrons, while frequency determines the maximum energy.
What does zero kinetic energy mean?
Check the status. It may mean no emission below threshold or the ideal threshold boundary.
Why is the stopping voltage numerically equal to eV energy?
An electron gains or loses one electronvolt for each volt of potential difference.