The photoelectric effect is a quantum electronic
phenomenon in which electrons are emitted from matter
after the absorption of energy from electromagnetic
radiation. Frequency of radiation must be above a
threshold frequency, which is specific to the type of
surface and material. No electrons are emitted for
radiation with a frequency below that of the threshold.
These emitted electrons are also known as
photoelectrons in this context. The photoelectric effect
was theoretically explained by Einstein who introduced
the light quanta. Einstein writes (Einstein, 1905) in
accordance with the assumption to be considered here,
the energy of light ray spreading out from point source is
not continuously distributed over an increasing space but
consists of a finite number of energy quanta which are
localized at points in space, which move without dividing
and which can only be produced and absorbed as
complete units. The linear dependence on the frequency
was experimentally determined in 1915 when Robert
Andrews Millikan showed that Einstein formula