Hertz and Lenard's observations, the laws of the photoelectric effect and why waves cannot explain them. Then Einstein's equation, the stopping potential and its graphs, the photon and its momentum, and the wave nature of matter with the Davisson-Germer experiment.
3 lessons, about 1 h 35 min3 simulations10 problems6 practice questionsPython in every lesson
Created by StemPy LabA photocell lets light knock electrons out of a metal plate. Its current is in proportion to the intensity of the light. The stopping potential depends on the frequency only, there is a threshold frequency, and the electrons leave with no delay. The wave picture of light cannot explain these three facts.
Einstein's equation turns the laws of photoelectric emission into a straight-line graph. The stopping potential, plotted against the frequency, has a slope that is the same for every metal. Millikan used it to measure Planck's constant. Counting the photons in a beam links its power to the current in a photocell.
A photon has energy and momentum . In 1924 de Broglie proposed that every moving particle has a wavelength . Davisson and Germer saw electrons diffract from a nickel crystal. The waves of everyday objects are far too short to see.
Log in to join the discussion.
Loading…