Claim: Albert Einstein discovered a phenomena.

The photoelectric effect is the emission of electrons or other free carriers when light is shone onto a material . Electrons emitted in this manner can be called photo electrons . The phenomenon is commonly studied in electronic physics , as well as in fields of chemistry , such as quantum chemistry or electrochemistry .   According to classical electromagnetic theory , this effect can be attributed to the transfer of energy from the light to an electron . From this perspective , an alteration in the intensity of light would induce changes in the kinetic energy of the electrons emitted from the metal . Furthermore , according to this theory , a sufficiently dim light would be expected to show a time lag between the initial shining of its light and the subsequent emission of an electron . However , the experimental results did not correlate with either of the two predictions made by classical theory .   Instead , electrons are dislodged only by the impingement of photons when those photons reach or exceed a threshold frequency -LRB- energy -RRB- . Below that threshold , no electrons are emitted from the metal regardless of the light intensity or the length of time of exposure to the light -LRB- rarely , an electron will escape by absorbing two or more quanta . However , this is extremely rare because by the time it absorbs enough quanta to escape , the electron will probably have emitted the rest of the quanta . -RRB- . To make sense of the fact that light can eject electrons even if its intensity is low , Albert Einstein proposed that a beam of light is not a wave propagating through space , but rather a collection of discrete wave packets -LRB- photons -RRB- , each with energy hν . This shed light on Max Planck 's previous discovery of the Planck relation linking energy -LRB- E -RRB- and frequency as arising from quantization of energy . The factor h is known as the Planck constant .   In 1887 , Heinrich Hertz discovered that electrodes illuminated with ultraviolet light create electric sparks more easily . In 1900 , while studying black-body radiation , the German physicist Max Planck suggested that the energy carried by electromagnetic waves could only be released in `` packets '' of energy . In 1905 , Albert Einstein published a paper advancing the hypothesis that light energy is carried in discrete quantized packets to explain experimental data from the photoelectric effect . This model contributed to the development of quantum mechanics . In 1914 , Robert Millikan 's experiment supported Einstein 's model of the photoelectric effect . Einstein was awarded the Nobel Prize in 1921 for `` his discovery of the law of the photoelectric effect '' , and Millikan was awarded the Nobel Prize in 1923 for `` his work on the elementary charge of electricity and on the photoelectric effect '' .   The photoelectric effect requires photons with energies approaching zero -LRB- in the case of negative electron affinity -RRB- to over 1 MeV for core electrons in elements with a high atomic number . Emission of conduction electrons from typical metals usually requires a few electron-volts , corresponding to short-wavelength visible or ultraviolet light . Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of wave -- particle duality . Other phenomena where light affects the movement of electric charges include the photoconductive effect -LRB- also known as photoconductivity or photoresistivity -RRB- , the photovoltaic effect , and the photoelectrochemical effect .   Photoemission can occur from any material , but it is most easily observable from metals or other conductors because the process produces a charge imbalance , and if this charge imbalance is not neutralized by current flow -LRB- enabled by conductivity -RRB- , the potential barrier to emission increases until the emission current ceases . It is also usual to have the emitting surface in a vacuum , since gases impede the flow of photoelectrons and make them difficult to observe . Additionally , the energy barrier to photoemission is usually increased by thin oxide layers on metal surfaces if the metal has been exposed to oxygen , so most practical experiments and devices based on the photoelectric effect use clean metal surfaces in a vacuum .   When the photoelectron is emitted into a solid rather than into a vacuum , the term internal photoemission is often used , and emission into a vacuum distinguished as external photoemission .