Photoelectric Effect Calculator
Einstein's photoelectric equation KE = hf - phi predicts the maximum kinetic energy of electrons emitted when light strikes a metal surface. Here h is Planck's constant (6.626 x 10^-34 J s), f is the photon frequency, and phi is the metal's work function. If hf is less than phi, no electrons are emitted regardless of intensity. This discovery earned Einstein the 1921 Nobel Prize in Physics and established the photon concept. Enter the photon wavelength (in nm) and the material work function (in eV) to find the maximum electron kinetic energy and stopping potential.
Photoelectric effect formula
E_photon = h * f = h * c / lambda
KE_max = E_photon - phi (if E_photon > phi, else no emission)
Stopping potential V0 = KE_max / e
Threshold wavelength = h * c / phi
h = 6.62607015 x 10^-34 J s, c = 2.99792458 x 10^8 m/s, e = 1.602176634 x 10^-19 C. 1 eV = 1.602176634 x 10^-19 J.
Common materials and their work functions
- Cesium (Cs): 2.0 eV, threshold wavelength 620 nm (visible light can eject electrons).
- Sodium (Na): 2.36 eV, threshold 526 nm.
- Aluminum (Al): 4.06 eV, threshold 305 nm (requires near-UV).
- Copper (Cu): 4.5 eV, threshold 276 nm (UV required).
- Platinum (Pt): 5.65 eV, threshold 220 nm (deep UV required).
Photoelectric effect: frequently asked questions
What is the photoelectric effect?
The photoelectric effect is the emission of electrons from a metal surface when illuminated by light of sufficient frequency. Einstein explained it in 1905 by proposing that light consists of photons, each carrying energy E = hf. An electron absorbs one photon, uses energy phi (the work function) to escape the metal, and the rest becomes kinetic energy: KE = hf - phi.
What is the work function?
The work function phi is the minimum energy required to remove an electron from the metal surface. It is a material property, typically measured in electron-volts (eV). Cesium has one of the lowest work functions at about 2.0 eV; platinum is near 5.65 eV. Only photons with energy hf greater than phi can eject electrons.
What is the threshold frequency?
The threshold frequency f0 = phi / h is the minimum photon frequency that can eject an electron. Below f0, no electrons are emitted regardless of light intensity. Above f0, increasing intensity increases the number of emitted electrons (more photons), but the maximum kinetic energy depends only on frequency, not intensity.
Why did the photoelectric effect disprove the classical wave theory of light?
Classical wave theory predicted that increasing light intensity would eventually eject electrons regardless of frequency, and that time would be needed to accumulate enough energy. Experiment showed: (1) no emission below threshold frequency no matter how intense the light; (2) emission is instantaneous above threshold; (3) KE depends on frequency not intensity. Only the photon model explains all three.
How is the stopping potential related to kinetic energy?
The stopping potential V0 is the reverse voltage needed to stop all emitted photoelectrons. The relationship is KE_max = e * V0, where e = 1.602 x 10^-19 C. Measuring V0 versus frequency and plotting gives a straight line with slope h/e, allowing determination of Planck's constant from experiment.
Official sources
- NIST CODATA 2018: Planck Constant.
- OpenStax University Physics Vol. 3: Photoelectric Effect.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.