6.2
eV
1.7
eV
1.7
V
275.56
nm
6.2
eV
1.7
eV
1.7
V
275.56
nm
The Photoelectric Effect Calculator determines the kinetic energy of electrons ejected from a metal surface by incoming photons, along with the stopping potential and threshold wavelength. The photoelectric effect, explained by Albert Einstein in 1905 in a paper for which he received the 1921 Nobel Prize in Physics, was one of the key pieces of evidence establishing the quantum nature of light.
When light strikes a metal surface, electrons are ejected only if the photon energy exceeds the work function (phi) of the metal — the minimum energy required to free an electron from the surface. Below the threshold frequency (or above the threshold wavelength), no electrons are emitted regardless of light intensity. Above the threshold, the maximum kinetic energy of the ejected electrons is KE_max = h*f - phi = hc/lambda - phi, independent of intensity. Higher intensity simply means more photons and therefore more electrons, not faster electrons.
Classical wave theory predicted that higher intensity light would eventually give electrons enough energy to escape regardless of frequency, and that energy accumulation would take time. Experiments showed the opposite: emission is instantaneous even for faint light, and below the threshold frequency, no emission occurs at any intensity. Einstein's photon model explained all observations perfectly.
The stopping potential V_s is the reverse voltage needed to stop all emitted electrons: e*V_s = KE_max. By measuring V_s as a function of frequency, Millikan (in 1914-1916) verified Einstein's equation and measured Planck's constant to within 0.5% accuracy, despite initially hoping to disprove Einstein's photon hypothesis.
The photoelectric effect underpins photodetectors, photomultiplier tubes, solar cells (which use the internal photoelectric effect in semiconductors), photocatalysis, and photoemission spectroscopy (ARPES) which maps electronic band structures of materials.
Photon energy: E = hc/lambda = 1240/lambda(nm) eV. Maximum kinetic energy: KE_max = E - phi, where phi is the work function. If KE_max less than 0, no emission occurs. Stopping potential V_s = KE_max (in volts, since KE_max is in eV). Threshold wavelength: lambda_threshold = 1240/phi(eV) nm.
If the photon wavelength is greater than the threshold wavelength, no electrons are emitted (KE_max = 0). Below the threshold wavelength, electrons are emitted with kinetic energy up to KE_max. The stopping potential equals KE_max numerically (in volts). Higher work function metals require higher photon energy (shorter wavelength) for emission.
Inputs
Results
UV light at 200 nm (6.2 eV) incident on copper (work function 4.5 eV) ejects electrons with up to 1.7 eV kinetic energy. The stopping potential is 1.7 V.
Inputs
Results
Cesium's low work function (2.1 eV) allows visible blue light (450 nm) to eject electrons. This is why cesium is used in photoelectric sensors that respond to visible light.
The work function phi is the minimum energy needed to remove an electron from the surface of a material. It varies from about 1.8 eV (cesium) to 5.7 eV (platinum). It represents the binding energy of surface electrons.
Each photoelectron interacts with exactly one photon. More intense light means more photons (more electrons emitted), but each photon still has the same energy, so individual electron kinetic energies are unchanged.
A retarding voltage applied to slow and stop emitted electrons. At V_s, even the fastest electrons (with KE_max) cannot reach the detector. Measurement of V_s gives KE_max = e * V_s.
Classical theory predicted that energy from light waves accumulates in an electron over time, so electrons would eventually be ejected at any frequency with sufficient intensity. In reality emission is instantaneous and frequency-dependent.
Only metals with low work functions: alkali metals like cesium (2.1 eV), rubidium (2.16 eV), potassium (2.29 eV). Most metals require UV light. Semiconductors show the internal photoelectric effect at lower energies.
A photon ejects an electron from a photocathode. This electron is accelerated and strikes a dynode, releasing several secondary electrons. After multiple dynode stages, one photon produces ~10^6 electrons — enabling single-photon detection.
No. In the photoelectric effect the photon is completely absorbed and an electron is ejected with all the photon's energy minus the work function. In Compton scattering the photon is partially absorbed and scattered with reduced energy.
Millikan (1914-1916) measured stopping potentials for different light frequencies using clean metal surfaces in vacuum. He found V_s = (h/e)*f - phi/e, confirming the linear relationship and measuring h to within 0.5%.
In semiconductors, photons with energy above the bandgap excite electrons from valence to conduction band without freeing them from the material. This is the basis of solar cells and photodiodes.
Angle-Resolved Photoemission Spectroscopy uses the photoelectric effect to map the electronic band structure of materials. By measuring emitted electron energies and angles, physicists reconstruct the dispersion relation E(k) of electrons in a solid.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
How helpful was this calculator?
Be the first to rate!
Electron Configuration Calculator
Atomic & Molecular Physics Calculators
Ionization Energy Calculator
Atomic & Molecular Physics Calculators
Electron Affinity Calculator
Atomic & Molecular Physics Calculators
Electronegativity Calculator
Atomic & Molecular Physics Calculators
De Broglie Wavelength Calculator
Atomic & Molecular Physics Calculators
Heisenberg Uncertainty Calculator
Atomic & Molecular Physics Calculators
