Timing the Photoelectric Effect

The Millikan Experiment

In 1916, Robert Millikan conducted an experiment using a photoelectric cell to measure the energy of electrons emitted when light strikes a metal surface.

He found that the maximum kinetic energy of the electrons was proportional to the frequency of the light, and that the number of emitted electrons was proportional to the intensity of the light.

Einstein's Explanation

Albert Einstein proposed an explanation for the photoelectric effect based on Planck's theory of quantization. Einstein suggested that light is made up of discrete packets of energy called photons.

When a photon strikes a metal surface, it can transfer its energy to an electron in the metal. If the photon's energy is greater than the work function of the metal, the electron will be emitted with kinetic energy equal to the difference between the photon's energy and the work function.

Applications of the Photoelectric Effect

• Photomultipliers
• Solar cells
• Photodiodes
• Charge-coupled devices (CCDs)