Photoelectric Effect Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/9/2026
The photoelectric effect ejects an electron from a material when it's illuminated by sufficiently energetic light: the maximum kinetic energy of the ejected electron equals Ek = E(photon) − W, where W is the material's work function. For 400 nm violet light on a material with a 2.3 eV work function, this kinetic energy is about 0.80 eV.
Explanation
The photoelectric effect, explained by Einstein in 1905 (which earned him the Nobel Prize in Physics), was one of the first experimental proofs that light behaves as discrete particles (photons) rather than a simple continuous wave. Each incident photon transfers its entire energy — calculated exactly as in our photon energy calculator, E = h×c ÷ λ — to a single electron in the material; if this energy exceeds the work function W (the binding energy holding the electron in the material), the electron is ejected with the remaining kinetic energy, Ek = E(photon) − W. Below this threshold, however, no electron is ejected, no matter how intense the light (how many photons are sent): this observation long puzzled classical physics, which expected that more intense light would always be enough to knock out electrons, regardless of its color. The work function depends only on the target material (alkali metals like sodium or cesium generally have a lower work function than metals like platinum, making them photosensitive at longer wavelengths, sometimes even in the visible range); this calculator takes it as an input rather than fixing a value for one specific material, to stay adaptable to any known material.
Example: 400 nm violet light, 2.3 eV work function
Inputs
Wavelength: 400 nm. Work function: 2.3 eV.
Calculation
E(photon) = h×c ÷ λ ≈ 3.0996 eV (same calculation as for photon energy). Ek = 3.0996 − 2.3 ≈ 0.7996 eV, since the photon energy exceeds the work function.
Result
The ejected electron has a maximum kinetic energy of about 0.80 eV.
Frequently asked questions
What happens if the photon's energy is below the work function?
No electron is ejected, no matter how intense the light: this is a threshold phenomenon, not a linear relationship that would give a negative kinetic energy. This calculator faithfully reflects that behavior by capping the kinetic energy at zero in that case, rather than displaying a physically meaningless negative result.
Why doesn't increasing the light's intensity help if its wavelength is too long?
Because each photon acts individually on a single electron at a time: increasing intensity increases the number of photons sent per second, but not the energy of each one, which depends only on wavelength. If a single photon's energy stays below the work function, sending more photons of that same wavelength will never change anything: it was this observation, incompatible with a purely wave-based view of light, that motivated Einstein's 1905 explanation.
Is the work function the same for every material?
No, it varies noticeably from one material to another: alkali metals (sodium, potassium, cesium) typically have a lower work function, making them sensitive to visible light, while other metals require ultraviolet light — a shorter, more energetic wavelength, see our wavelength and frequency calculator — to produce the same effect. That's why this calculator leaves this value as an input rather than fixing it for one particular material.