Quantum
Early History | Planck's Contribution | Einstein's Contribution | Bohr Atom | Wave Mechanics | Matrix Mechanics | Quantum Meaning | Uncertainty | Quantum Results | Developments | The Future | Two Holes | Quantum Time Waits for No CosmosThe next important developments in quantum mechanics were the work of German-born American physicist and Nobel laureate Albert Einstein. He used Planck's concept of the quantum to explain certain properties of the photoelectric effect—an experimentally observed phenomenon in which electrons are emitted from metal surfaces when radiation falls on these surfaces.
According to classical theory, the energy, as measured by the voltage of the emitted electrons, should be proportional to the intensity of the radiation. The energy of the electrons, however, was found to be independent of the intensity of radiation—which determined only the number of electrons emitted—and to depend solely on the frequency of the radiation. The higher the frequency of the incident radiation, the greater is the electron energy; below a certain critical frequency no electrons are emitted. These facts were explained by Einstein by assuming that a single quantum of radiant energy ejects a single electron from the metal. The energy of the quantum is proportional to the frequency, and so the energy of the electron depends on the frequency.
Quantum
Early History | Planck's Contribution | Einstein's Contribution | Bohr Atom | Wave Mechanics | Matrix Mechanics | Quantum Meaning | Uncertainty | Quantum Results | Developments | The Future | Two Holes | Quantum Time Waits for No Cosmos