Photoelectric Effect Calculator

The photoelectric effect is a quantum phenomenon in which electrons are emitted from a material's surface when it absorbs electromagnetic radiation — such as visible light, ultraviolet, or X-rays. It was first explained by Albert Einstein in 1905, an achievement that earned him the Nobel Prize in Physics in 1921. The key insight is that light behaves as discrete packets of energy called photons, not as a continuous wave.

Einstein's photoelectric equation is Kmax = hf − φ, where Kmax is the maximum kinetic energy of the emitted electron, h is Planck's constant (6.626 × 10⁻³⁴ J·s), f is the frequency of the incident light, and φ (phi) is the work function of the metal. If the photon energy hf is less than φ, no electrons are emitted regardless of light intensity.

The work function (φ) is the minimum amount of energy required to liberate an electron from the surface of a metal. It is a property of the material and is typically measured in electron-volts (eV). Metals with lower work functions (like cesium at 2.10 eV) eject electrons more easily than metals with higher work functions (like platinum at 5.65 eV).

The threshold frequency (f₀) is the minimum frequency of incident light required to eject electrons from a metal surface. It is calculated as f₀ = φ / h. Light below this frequency cannot emit electrons regardless of its intensity, because individual photons carry insufficient energy to overcome the work function.

The stopping potential (Vs) is the voltage needed to bring the emitted photoelectrons to a halt, thereby measuring their maximum kinetic energy. It satisfies the relation eVs = Kmax, where e is the elementary charge. A higher photon frequency (above threshold) results in a higher stopping potential because the electrons are ejected with greater kinetic energy.

No — and this was one of the surprising aspects of the photoelectric effect that classical wave theory could not explain. The maximum kinetic energy of emitted electrons depends only on the frequency of incident light, not its intensity. Increasing intensity means more photons hit the surface (producing more electrons), but each individual photon still carries the same energy hf.

You can enter either the frequency (in THz) or the wavelength (in nm) of the incident light — the calculator converts automatically using the relation c = λf, where c is the speed of light (≈ 3 × 10⁸ m/s). Select your preferred input mode at the top of the calculator. For example, 400 nm corresponds to approximately 750 THz (violet light).

Classical wave theory predicted that any frequency of light, given sufficient intensity, should eventually eject electrons — but experiments showed this never happens below the threshold frequency. Einstein resolved this by treating light as photons (particles), each carrying energy E = hf. Only photons with enough individual energy (above the work function) can free an electron, proving light has quantised, particle-like behaviour.